So in order for her to be colorblind (well, assuming it's the more common red/green version) she has to have received the colorblind X chromosome from both her father and you. Does your family have color blindness? 3/4 of my brothers are colorblind and I am a carrier.
I would have her tested-has she seen an eye doctor before? By age 3 I would probably have her seen just for a baseline and general eye health, plus they can evaluate for the colorblindness. My brothers all went through school just fine with zero accommodations for their color issues. It's certainly something to be aware of, but not a crippling disability, really.