Colour blind aged 4?

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/

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.

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.

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

There are simple picture type tests you can do on line. That might be easier as a start.

It’s genetic passed down from the males through the females.My father was colourblind and my son is too.Hasn,t really been an issue except when he was interviewed for a job involving electrical wires.He didn,t get it.
No more boys in the family he has three daughters.

I too am colour blind and have had countless agreement about the colour of things! It was picked up til I was an adult so my advice is get it diagnosed just so teachers can be alerted.

There are men in my family who are colour blind.

My grandson found geography very difficult as unfortunately it's not a protected characteristic so had no help in exams to know which area of the maps were pink/red/green etc

Some jobs will be outside what's "allowed" - Airline Pilot,
​Air Traffic Controller ,Military Roles involving combat, piloting, or bomb disposal.
​Electrician / Electronics Engineer.
​Train Driver, Sea Captain...

Reading LED Indicators can be difficult, dropping things on the floor, choosing clothes to wear together, grouping things by colour (obviously).

My husband was teased a lot at school about it "what colour is this".
He bought our grandson pencils and felt tips with the name of the colour on them so life was a bit easier in colour-coded maths/science/geography etc.

Art is also problematic ' unless you embrace it.
In art, a "limitation" might just be an entirely new way to be creative.

You can now get specialised color-blind glasses, (and phone apps that read colors aloud).

...and since traffic lights now have white lines round the edges at least you can be safe driving at night!

Colour-blind individuals don't normally have "color distraction." Instead, their brains rely heavily on luminance (brightness), texture, shape, and outlines. This makes them good hunters (and spotters of needles in a haystack.)

This effect is so pronounced that during World War II colour-blind spotters were often taken in aircraft because they could easily see through camouflage netting that fooled regular soldiers.

There are lots of versions of what we loosely call colour blindness.
All have their own peculiarities.

My uncle was red/green colour blind. It wasn't until he started school and painted a picture of a red plant in a green pot that it was picked up on.
He went on to become a fireman and drove the fire appliance without incident. He learnt the sequence of the traffic lights so didn't need to know the colours.

My DS was only discovered to be colour blind when at the age of 30 something he applied to join the police. He failed their strict test and was rather shocked.

Labelled pencils etc for your DGS sounds like a good idea of NotSpaghetti's