I don't think the app is meant to be a whole color scheme design tool, so much as a helper that solves the specific question: "What is one shade lighter of this color?". "How about two shades".
Exactly. I made 0to255 to solve the "I need a slightly lighter color" problem, which is actually a really frequent one. There are already really awesome tools for color inspiration like those on http://www.colourlovers.com/
