Many people assume that colourblindness is a condition where you only see black, white, and grey. This is a common misconception. In actual fact, it is extremely rare to be totally colourblind, most colourblind people can still see colours but the most common problem is people that have trouble seeing different shades of red or green.

So what causes colourblindness?
(Taken in part, by colourvisiontesting.com)
The human eye sees by light stimulating the retina (a neuro-membrane lining the inside back of the eye). The retina is made up of what are called Rods and Cones. The rods, located in the peripheral retina, give us our night vision, but can not distinguish color. Cones, located in the center of the retina (called the macula), are not much good at night but do let us perceive color during daylight conditions.
The cones, each contain a light sensitive pigment which is sensitive over a range of wavelengths (each visible color is a different wavelength from approximately 400 to 700 nm). Genes contain the coding instructions for these pigments, and if the coding instructions are wrong, then the wrong pigments will be produced, and the cones will be sensitive to different wavelengths of light (resulting in a color deficiency). The colors that we see are completely dependent on the sensitivity ranges of those pigments.
5% to 8% (depending on the study you quote) of the men and 0.5% of the women of the world are born colorblind. That's as high as one out of twelve men and one out of two hundred women. I am going to limit this discussion to protans (red weak) and deutans (green weak) because they make up 99% of this group.

So how can I tell if my child is colourblind?
That's easy, just click here. It's a fun and easy test for you and your child to do. Provided they know their colours and are able to count to at least 10. Or, if they dont, heres a pediatric colourblind test which is designed for 3 to 6 yr olds.
Here's a page I found interesting, its how colourblind people see the world. I found it amazing, which is what made me write this article.

I hope this has taken a bit of the confusion away from some parents out there as to whether their kids can see all or just part of the rainbow.  Take care everyone :)