Colour blind aged 4?

Sorry I didn’t mean ‘has he just developed it?’
That was misleading.

Oh we know when he’s having us on or being contrary.
This is a genuine issue.

I will advise DD to seek opticians appt. Thanks

I am colour blind and have been since birth. It can be tested for quite easily. It is a life long condition: I can't say it has affected me greatly, although I did buy a pair of black trousers once that were brown.

I think it is something you are born with, so age has nothing to do with it.
Or he may be teasing you.
Smarties can be a useful tool in establishing whether he has a genuine problem or is enjoying being contrary.

Your DGS has probably been colour bind since birth. The standard form of colour blindness is the green/red problem you describe. Take him to an optician, explain the problem and take his advice.

Here is a link to an NHS site that can help
www.nhs.uk/conditions/colour-vision-deficiency/