- Question: With text overlapping a picture of a person with a black-and-white-striped shirt. No matter what fixed "color value" you choose or what system you express it in (RGBA, APCA, etc.), you're going to have some of your letterforms appear in an area of insufficient contrast. (e.g. if you choose a dark color, your letters won't be readable on top of the black shirt stripe and visa versa for a light color).
Funny you should mention this. One of the experiments that we use in the lab for determining the middle point of perceptual contrast, specifically involves putting text against stripes of black and white.
The spatial frequency, in other words the size of the stripes relative to the font, is substantially important. As is the overall size and weight of the font. If I understand what you are asking for — maximum contrast at any given point, the results may not be what you expect. Here are examples.