A friend of mine forwarded this link to me which has some suggestions for colorblind hikers who have trouble identifying blazes on trails. The article outlines one particularly interesting way to help identify the colors of the blazes: carry paint samples to reference the blazes against. It covers how to make these and how to use them as well as some other tips to help colorblind hikers.

Another approach that I think would work well would be to carry colored filters to aid in identifying the blazes. A blue filter would make a blue blaze look brighter and a orange filter would make orange blazes brighter for example. A tool like the Seekey could also be useful in identifying the color of the blaze. Good lighting will help when comparing the blaze to the paint sample or when viewing it through the filter, so if it's too dark a flashlight (preferably not one of those cheap purply LED ones) may obviously be useful.

Source:
Helpful Suggestions for Color Blind Hikers, the New York Outdoors Blog

(I own a copy of one of their books, 200 Waterfalls in Central & Western New York)