This should be a simple question, but I haven\'t been able to find a way to make it work.
Essentially, I have a silly localhost page that I use in my webdevelopment.
"Contrast" is a loaded word. If you just care about being able to read the text, then one easy way is to work in a luminance-based color space like HSL, and pick foreground and background colors with big differences in luminance.
The conversion between HSL and RGB is well-known--see Wikipedia for the details.
If you're talking about actual color contrast, it's not nearly as cut-and-dried (there are a lot of perceptual factors that, as far as I know, haven't been reduced to a single colors space), but I suspect you don't need that level of sophistication.