heres something that i know a bit about. DH & DS are both blue/green colour blind, but i dont think that DD is - we have given her the test (shes 3 & quite capable of doing the test)
It is genetic, so if there are no other males in your family that are colour blind, then there is NO chance that your kids can be. The males must be directly blood related
Colour blindness cannot be detected by placing 2 different cards - say one blue & one green, next to each other. It is such a complicated thing.
There are 2 basic types of colour blindness - red/green & blue/yellow. From there, they break down into many diffent degrees & descriptions. waaay too complicated. Depending where they sit on the scale, will depend on exactly what they see. So, DH sits on the scale of a 4 - scale is to 5 - so he is pretty bad, DS sits at 2, so not so bad. They get reds & greens confused when they are together - IYKWIM - so for an easy example, a green tree with red flowers... they cannot distinguish between the flowers & the leaves, yet if you put a red solid stripe on a card next to a card with a green solid stripe, they can pick the difference & answer correctly. It is such a complicated condition. Dont even talk to me about shades of colours... argh....
for toddlers, i have found the easiest way to detect colour blindness (red/green only, but that is the most common one) is to put some red pegs in the grass & ask the child to pick up the pegs for you. they will either have difficulty finding them, or just wont be able to see them at all.
But like i said, if there is NO history of it in your family - so you or your partners fathers, grandfathers, being colour blind, it is impossible for your children to be.
The expectation for children to learn & recognise colours is 5, so dont stress!