I knew that about colourblindness (my old boss is colour blind, and I had to produce lots of pictures for our work).
Most the colourblind men I know confess to struggling to dress in matching colours (by their own admission). This is the only thing about colourblindness in DC that might worry me
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My grandfather was a qualified airplane pilot. Also a general in the US Army -- he was an expert in desert warfare and trained the likes of Colin Powell and Norman Schwarzkopf (good mate). My grandfather was also RG colourblind.
Since his son (my dad) has full colour vision and I am female, from what I understand about the genetics it's highly unlikely that any of my children would be RG colourblind, although I also understand that the genetic mutation can occur in any generation.
No, I think DS3 is just stubborn. Also speech delayed which makes it harder to talk about or understand the words for colours. DH thinks he's deliberately being contrary, insisting that everything must be "bwooo" for instance.
(Contrary, who, my children? At least I read somewhere that contrariness is a sign of intelligence (clutching at straws, here)).