Terminal programs usually let you alter the palette of colours used by applications. However, this isn't really flexible enough, particularly for people with odd monitor setups or vision problems. For example, many programs use the dark blue colour in xterm on a black background, which isn't particularly easy to read; the obvious fix is to make it a brighter blue, but that then causes problems for programs that use it as a background colour or against a light background.
I'd like a terminal program that allowed me to specify what actual colour an xterm colour should be in different contexts. This would allow me to specify that the dark blue should be its normal colour when used against a light colour, but should be a bright blue when used against a dark colour.
The obvious way to implement this for the normal 16-colour palette would just to be to create a 16x16 lookup table on startup for all the possible colour combinations; this would avoid having to follow the user-specified rules for each colour change.