Yes. This is unusual, as the causes would more likely cause a degradation of vision in general, e.g. glaucoma, cataract, diabetic retinopathy, optic nerve neuropathies.
If you are experiencing adult onset colorblindness,
o Check your diet. Are you getting all the vitamins and minerals? Take a daily vitamin / mineral pill daily. Start right now, don't wait.
o Call your ophthalmologist and, uh, see him. (If you're in the United States, call your primary care physician and ask for an in-plan ophthalmologist referral ... and this is why "plans" suck.)