This utility will be able to convert color schemes across VIM, irssi and Mutt. Given that irssi and Mutt are terminal based, the schemes will need to be within the 256 colour palette.
Vivify is able to produce a good looking vim colourscheme quickly, which could be used as the base.
I've already added an example muttrc colour file which has most of the items you would want to be coloured.