How much does the color of an OWB holster matter for CCW? If it's a darker color, than I suspect it'll show through a t-shirt unless a cover-up is worn. Therefore, would a lighter color holster be in order?
I like to go with colored t-shirts or shirts of a slightly thicker fabric where the fabric is opaque no matter what color it is. I sometimes wear a sleevless white cotton buttondown shirt as a concealment vest and the fabric is such that you can't see through it even though it is white and I have a black gun.
Another thing to consider is to get a shirt with a busy patterned design on it. Patterns break up printing and printing shadows.
Summer time calls for my Galco SOB. It is black, but no one has called my attention to it, except one police officer at a State Park. He asked if I was armed, but I replied to the negative. He then stated that he had noticed a bulge in the middle of my back as I had bent over. I raised my T shirt only to reveal an empty holster. (firearms are not permitted in State Parks). Asking where the firearm was resulted in my telling him that it was in my truck locked up. This satisfied the officer, and he went on his way.