For a shell or a shirt, I would think the same stores would be good places to start. As for color, it doesn't absolutely have to be white, cream or light blue. I would think a French blue would be OK. Maybe even gray. While I might not wear pink, if it really enhances your complexion in, say, a black suit, a pale pink might be fine. I just wouldn't do anything shiny or too colorful, e.g., jewel tones, fuchsia, hot pink, etc. Honestly, as long as your suit is conservative, you can have a bit more leeway with the top. Again, I'm talking about an initial interview. Of course, when you've been working somewhere for awhile and earned your stripes, you can certainly branch out and be a bit more fashion forward. In an initial interview, however, there is simply no upside.