Anyone know if colour-blindness in rare in Thailand? Doctors here act like it is, and Thailand is the only country I've heard of that has a colour-blindness test when applying for a driving licence.

You can take a look here (in Thai but don't think it will be a problem for you). My cursory interpretation is that 5-8% of males born have some degree of color blindness and .5% of female. Of course I may be way off course in my interpretation and it may be in general and not Thais specifically.

http://www.thaiclinic.com/medbible/colour_blindness.html

I don't have population statistics but two out of about 10 guys in my office are colour blind, so chances are it is not that uncommon.