LET THERE BE WHITE; YES,BUT DO YOU WANT APPLE WHITE.

Byline: PETER SILVERTON

It was barely past nine on a wind-whipped Chelsea morning.

Patrick Baty, a thin-faced man in early middle age and a white lab coat whose watch was stuck at barely past eight, had already talked - with infectious enthusiasm - of Goethe. `His writings on colour are really what he wanted to be remembered for. All our theories of colour are centred on his work, you know.' He'd talked of his 15-year career in the army and the 12-minute bicycle ride from home to Paper And Paints, his small shop and workshop just off the Fulham Road. Of the impossibility of obtaining top quality Cypriot raw umber since Turkey invaded the island and of the impossibility of some of the customers who find their way to his shop.

`Thoroughly confused' was a phrase he used.

Then he got on to the matter at hand. White paint. Or rather, I hesitantly suggest, white paints - rose white, off-white, hallelujah white and so on.

He was having none of that notion. `Forget about what you might have heard,' he said, with the precision of someone whose PhD thesis was Methods And Materials Of The Housepainter In The 18th And Early 19th Century. `If we are using different descriptive languages, there's no point of contact. So let us agree on certain terms. There is brilliant white paint - which has optical brighteners in it. There is white - which doesn't. And after that we're talking about coloured paint.'

He pointed to a Sanderson paint chart. `Look at that colour, Matterhorn. It has a pale hint of Palmyra, a muddy green. Matterhorn is already very pale but we can make it twenty times as pale as that. But it would still be a coloured paint. White itself is achromatic.'

What about his lab coat then? That's white, isn't it. `Mmm,' he said. But it's not the same white as the window frame, is it. `Mmm,' he said again, a little uncomfortable with the intrusion of the real world into the paint world. `Why I find this so difficult is that while I agree in general terms that my coat is white . . .' His voice tailed off and, in search of a resolution of sorts, he crossed the room to his expensive new gadget, a Minolta spectrometer - `cost about the same as a big black motor car' - hooked up to a PC running an application called QuickMatch. Test any colour with the spectrometer - it's fully portable, about the size of a biggish paintbrush - and the computer will work out how to make a paint that colour.

Not roughly that colour but exactly that colour - vital for Mr Baty's work on restoring some of our finest old buildings.

He placed the edge of his white lab coat under the spectrometer and took a reading. `Mmm,' he said. The computer analysed the colour. `I've never seen a curve like that. Don't even know if the computer can match it,' he said with gloriously schoolboyish thrill and set QuickMatch to work. It did its stuff. Take some basic white paint, add minuscule amounts of yellow oxide, blue, violet - `that's probably the optical brightener in the washing powder' - and you too could have walls the colour of Mr Baty's lab coat.

Exactly the colour of Mr Baty's lab coat. Which is a white. Unless you're Mr Baty, of course.

`Oh yes,' said Min Hogg. `People go to the gallows still thinking about …