My father is colourblind (red/green) but I have no issues at all.
My DS1 however was diagnosed as colourblind when he was almost 7. He practically can't see the colour green and has issues with many other colours like he will see some shades of green as grey, bolder greens he can see... he sees some shades of red as purple, sometimes green he sees as orange etc.
The test he took was some pictures and he was able to see numbers or shapes in the dots... then they had a little machine thing that looked into his eyes at the colour cones where it was noticed my son has only 3 green cones when he is meant to have many more.
I will need to test DS2 for this when he is old enough.