Try to use all colors supported by the terminal.

This uses `tput colors` to get the number of available colors and `tput setaf $color` to set it.

I made the change because in my current setup, with 6 or 7 processes, they very often get the same gray color. Increasing the range of colors worked for me. I have 256 colors in my terminal. This approach should also degrade well if you have only 8 (kind of depends on your background color too).

I hacked this quickly, but let me know if you like it and we can think of a good way to do this.