I was at a talk the other day where the speaker asked how many colours of the rainbow there were. The conventional answer is seven - red, orange, yellow, green, blue, indigo, violet. Where, then, was crimson and turquoise?

We were reminded that Newton, the first to split white light into a spectrum using a prism, had a thing about the number seven and was determined to see seven colours. Personally, I don’t think indigo pulls its weight. It’s the chromatic equivalent of the planet Pluto (there were seven known planets in Newton’s time) and needs to get the Weakest Link treatment.

How many sciences are there? The conventional answer in a Scottish school is three, though I once worked with a principal teacher who claimed that chemistry was “that small branch of physics concerned with radioactivity and the electrostatic interaction between atoms”.

Lord Rutherford claimed that “in science, there is only physics; all the rest is stamp collecting”. That was in the days when biology stopped at taxonomy. Or do I mean taxidermy? The subject certainly had a limited appeal for me due to the large number of facts I had to stuff into my head.

Just when I thought I had ammo for an attack on the overly enthusiastic way some teachers are willing to pigeonhole themselves as physicists, chemists and biologists, another talk came along. This was by a weel-kent earth scientist from Our Dynamic Earth in Edinburgh. His subject, he reckoned, was well placed to support the cross-curricular nature of A Curriculum for Excellence.

By way of an illustration, he had a slide with earth sciences as a kind of lintel atop three pillars labelled with the conventional three sciences. But what was this? The three pillars were red, blue and green, the primary colours that can be mixed to produce all the others.

The introduction of faculty systems has coincided with an increase in science teachers wishing to teach only their own discipline. Perhaps “coincided” is the wrong word. It implies that there is no causal relationship between the two events and this may not be the case. Is either of these developments a good thing, or is something a little off colour happening here? I’ll come back to this another day when I’ve worked it out myself.

Meantime, imagine a world without yellow.

Gregor Steele associates a different colour with each physical concept, something that got him funny looks at a writers’ group.