I use my camera in B&W mode to see values instead. I know some people have been hassled for taking pictures in stores but so far nobody has ever seemed disturbed by me doing this. I don't even usually take a picture, just look at the screen in B&W. (Maybe they can just tell what I'm doing? It's probably pretty obvious since I'll be stacking and re-stacking bolts of fabric between looks...)

I have the green and the red value finder sheets, but I rarely use them at home and I never have them with me in stores. But I almost always have my camera. If it's my own fabric at home I do usually take pictures and then look at them on my monitor so it's easier to see. In a shop, I usually just look at the screen.

I use the B&W function on my camera and then view the pictures on my computer when using fabric from my stash.

I don't have the glasses but do use a value finder. Use red for all fabrics except red, then use green for red fabrics. It takes away the color and replaces it with the value of the fabric. Some prints can get tricky to figure out where they go in a progression from light to dark. Remember value does most of the work but color gets the credit.