"I remember being in awe of the idea that a piece of green paint could be a tree as well as green paint at the same time," he says.

"That's just a wild idea! If you put this green paint on a piece of paper and it's a tree and it's green paint at the same time, it's pretty cool! And it's an idea that has me cut loose, that things can have this duality."

He's been pursuing colour throughout his artistic career ever since, from the collages and Islamic patterns he created back in the 1990s, to his ever-growing collection of vases - "particular vases: they should be symmetrical and solid-coloured". Colour and geometry are the mainstays of his work - a large body, with works scattered across Australia, India and Hong Kong. He's now in his late 40s, and while his work has veered in form and medium over the years, everything has changed, but nothing has changed.

Just don't ask him where he stores the hundreds of books he collected over years purely for the colour of their spines. They certainly looked amazing in an installation created for a survey show in 2006. And they are probably getting on famously with the hundreds of "symmetrical and solid-coloured" vases he also has stored somewhere. It's a constant peril for someone who naturally finds humour and beauty in the ordinary and the humble.

There is certainly no room for them in his house, an unprepossessing structure in Canberra's south which, inside, is already filled to bursting with art. Sequeira - cerebral, impeccably dressed with a gravelly voice and an easy laugh - has lived here for 18 years, almost as long as he has lived in Canberra. In that time, he has worked at several cultural institutions, set up in his own gallery, thrown himself into the local community and, most importantly, steadily worked on his artistic practice.

And now, it's time to go. He has just accepted a job at the Latrobe Regional Gallery in Morwell, Victoria, and, as he prepares to pack up his well-established life here, he's not exactly sad to leave.

"I've really thrown myself into Canberra," he says.

And Canberra will always be a part of him, a state of being he predicted long ago, when he first began working at the National Gallery of Australia.

Born in New Delhi in 1966, Sequeira moved with his family to Melbourne when he was four. His parents were teachers, and made the decision to move to Australia to take advantage of the severe teacher shortage in Victoria in the early 1970s. Growing up in Essendon, where his mother still lives, Sequeira followed his parents into a teaching career, and taught in various Melbourne primary schools. He also studied art history part-time, focusing on Italian painting 1200-1600. He loved it, and, more to the point, it stood him in good stead when he finally had his first European adventure at the (comparatively) ripe old age of 25.

It was 1991, and after travelling the world, David the primary school teacher returned to Australia with a new life plan.

"It was very, very clear to me, when I left Europe, that I needed to play the cello, be an artist and work in a museum," he says, leaning back on the black leather couch in his art-filled living room.

He met at least two of those goals.

"I played cello really badly for two years - really, really badly," he says, straight-faced.

"I started painting and I taught full-time and went back to uni and did a post-graduate diploma in art and curatorial studies at the University of Melbourne."

When a job came up in public programs at the National Gallery in Canberra in 1995, he jumped at the chance, and not only because Canberra was home to his cello idol, David Pereira.

"That was a really exciting time at the gallery - it was an exciting time for galleries in general, because the '90s was that time when museums really threw themselves into access for people," he says.

"In the late '90s, we started to look at getting online and the digital side, but we also started looking at events that were family-directed. We began not just looking at who came to art galleries but who didn't come, and why they didn't come, and began to develop programs for young people, programs for older people, programs for people from different languages, culturally specific programs."

It was an absorbing job, but it was when he received a personal, handwritten letter from then director Betty Churcher during his first year there, thanking him for his work, that he realised he was on to a good thing. He worked at the gallery for eight years, and says he took every opportunity to learn from the best.

"You had a relationship to art and to curators and to what I was educating young kids about," he says.

"In the bulk of that first year my priority was with school kids, but even when I became a manager in that area I kept working with kids. That's actually a pretty important part of what I think museums are about, or certainly what I can offer inside museums."

He also, in that time, did several artist residencies, including a stint in the Australia Council studio in Paris. And then, in 2002, a collector bought 10 of his works in one go. It was time, he said, to switch focus.

"It was the most money I'd ever had," he says.

"It was a corporate collection in Sydney. And I had an opportunity to really give myself to my artwork, so I left the gallery, and painted, and did short-term contracts with people."

In the intervening years, he has worked at the National Portrait Gallery; Old Parliament House; the National Film and Sound Archive; Parliament House; set up his own gallery, Everything Nothing Projects; and, with his partner Ben O'Reilly, organised the Canberra Pride SpringOUT festival. He's had several exhibitions in Canberra, and a major survey show at John Curtin University gallery in 2006, complete with catalogue and full-length essay.

And, as he's in no way naive about the kinds of people who are likely to buy his art; he has always made a point of looking beyond Canberra.

He's travelled, acquired art dealers in Perth, India and Hong Kong, and even developed a corporate training program that uses painting and drawing as a metaphor for business development and staff management.

But in fact, the last few years have had their fair share of stress. Like many artists, Sequeira has had various day jobs in the arts sector, and not much security in between.

"Canberra, I would argue, more than any other city in Australia, is susceptible to government policy, given that a big slab of our population is public service," he says.

"But also, there's no industry here as such, so even slight shifts in policy have really big impacts for us. I've spent a long time working in cultural institutions and they're feeling the pinch of that."

But he says the best part about being effectively out of work for the past nine months is that he has thrown himself into his art. He does most of it at home, on his kitchen table or in his study, surrounding by an eclectic range of art by other people.

"I didn't go to art school, so I don't see myself as a painter, I don't see myself as a photographer or a printmaker or any one of those things," he says.

"If you ask me, 'What's your medium?', even though they're not mediums, I would say colour and geometry, and then whatever form that takes is the form it takes for that project."

He has made videos and large-scale photographs, as well as paintings, prints and sound installations – with the consistent thread of colour and geometry throughout his work.

"The form's changed a little bit and in truth, my interest's moved closer to the contemplative," he says of the evolution of his work.

"They're tonal and I'm interested in the sublime."

He has a large-scale work in Colour Music, a current show at the Drill Hall Gallery. Made up of 48 pieces, Symphonic Poem ties in with the show's examination of synaesthesia through colour and music.

"What I wanted to create was that the work is literally the sum of the individual parts, a kind of orchestration of a whole range of tones and subtleties and colours," he says.

"I didn't set out to illustrate a symphony or anything like that, my point is that I'm interested in how a whole range of forces come together to create something universal.

"For me, it's quite obvious that those sorts of ideas run parallel with ideas of music. The idea that several notes together can make a chord, that one note played next to another note creates a particular mood and experience – it's a sensory experience that's not dissimilar to one colour placed next to another colour."

It's not surprising that his works usually sell to other artists, architects and designers, sometimes in suites, and his dealer in New Delhi has introduced him to a whole range of European collectors. And his work sells for a lot more in India than it ever would in Australia. Although he is Indian-born and travels there often, he often feels backward when brushing up against the types of people who can afford his art over there.

But this is the reality of being an artist in Australia, and especially Canberra.

"I can put my hand on my heart and be really truthful - people in India value my art more than they value it in Canberra. It's a hard thing to say, but in terms of buying it and wanting to own it … it's the reality of it," he says.

"At some point we have to deal with the reality that people value a work of art to an extent that they want to live with it. That they see something that can contribute to their lives and they want to have that. This is not just about my art, this is about art in Australia and in Canberra, and about the nature of selling art.

"I don't think it has anything to do with price. I've been lots of shows in Canberra of really good art, really cheap, good art, under $1000, under $500, quality art by artists that you know are going to be famous, and there are still paintings left on walls, there are still people saying, 'Could you give it to me a bit cheaper?' "

Putting his money where his mouth is has always been a point of pride to him. He points to a large, murky abstract across the room – the first work he ever bought, at the age of 20, a 1965 abstract by the Australian artist Roger Kemp.

"I've got to say I'm pretty proud of buying something that tough at 20. It was my first pay check, and then my second pay check went to pay for the framing," he says.

"I made a commitment when I first started work that a certain percentage of my wage would be about buying art. Because there are lots of privileges in life and living with art is one of them. It's the one that I've got the best access to. I hardly eat out, you've seen my garden, it's a mess, I live in 90 square metres of house, I live really, really modestly. But I've got great art."

Colour Music is showing at the Drill Hall Gallery until September 28.