Long ago, in a school art exam, I attempted to mix the colour of a sponge cake - part of the still life set before us. "Why did you paint it green?" the invigilator later asked.
I knew I had a problem with colours, but it wasn't until my national service medical that someone identified it using the Ishihara test. Where most people have red, green and yellow receptors in their retinas, enabling the brain to create the full spectrum of colours, I have virtually no green receptors.
The shorthand term for this is colour-blindness. This is very misleading, because I do see colours, but not as most people see them. Has it caused me problems? Not really, but then I have never aspired to careers that would have been closed to me - aviation, for example.
I have difficulty with all forms of colour-coding, such as maps and graphs, and I curse those clever designers who select text and background colour combinations that make the results invisible to me. My wife helps me to choose my clothes and will not let me out in my red trilby, which is apparently more attention-grabbing than I think it is. But none of that is much more than inconvenient. I know my limitations, as do the people around me, and I go for long periods not thinking about it.
But what can teachers of children who are colour-blind do to support them? One boy in 12 and one girl in 200 has some form of colour vision deficiency, averaging at least one in every classroom.
Colour vision researcher Leticia Alvaro Llorente of the Universidad Complutense of Madrid has encountered every kind of case, from those who reach adulthood unaware of any problem to those who have struggled since an early age.
"In the worst cases, they have had to deal with teachers thinking that their difficulties stem from a learning disability or misbehaviour. Most of these problems could be solved very easily with a redesign of the tasks," Llorente says.
Her advice to teachers is to think inclusively, and not to put children in a position where they are required to recognise and match colours in order to cope with classroom work. It takes little effort to put labels on colour-coded charts and objects, or to use symbols and names instead of colours, she explains. The room can still be beautifully colourful, providing that a colour-deficient child can work confidently in it, on as near to equal terms as possible.
The perfect blend
There are, of course, lots of details to think about. Coloured pencils, for example, come in sets of 12, many of which I have never been able to tell apart. I vividly remember hopelessly attempting to draw multicoloured graphs. Some manufacturers print the name of the colour on the pencil. Others do not, so the teacher or teaching assistant needs to label them.
Most bewildering - apart, perhaps, from colour-coded maps in geography - is the concept of mixing colours, which crops up in art and in the study of light in physics. Colour-blind children can understand and memorise principles and physical laws about colour and the colour spectrum, but the teacher cannot assume that everyone in every class will be able to see colours clearly. The worst-case scenario here, Llorente says, is that a child will be thought of as stubborn or slow to learn.
Anna Franklin, professor of visual perception and cognition at the University of Sussex, adds that there's a particular issue in early years settings because children of 2 or 3 are only just beginning to learn the names of colours.
"I get emails from parents who are worried that a young child cannot name colours, but at that age most children find it difficult anyway, and there are no reliable colour vision tests for children under 4," Franklin says. Early years practitioners, then, need to be particularly aware of potential issues.
Yet there's no need for teachers to panic. I would suggest, after many years of living with the condition, that it's important to preserve a sense of proportion. Colour vision deficiency has specific effects but it is not disabling in a general sense and should not be thought of in that way.
Llorente sums up the issue for teachers perfectly: "People affected by colour vision deficiencies are not very disadvantaged in most tasks, but it would be better that educators be aware of the problem."
Gerald Haigh is a former teacher and headteacher, and a freelance writer on education
The Colour Blind Awareness Organisation offers plenty of advice for parents and teachers.
The Colour Group at the University of Sussex offers up-to-date research on colour cognition. www.sussex.ac.uk psychologycolour