For my new election maps, the color code is as follows: (in RGBA format)
Dem (Re-)elected: 000080ff
Dem takeover: 0000ffff
Dem retired: 3299ffff
Dem up for election: 3072afff
GOP (Re-)elected: 800000ff
GOP takeover: ff0000ff
GOP retired: ff8080ff
GOP up for election: d53034ff
Unkwown (future election): 00ff00ff
Indep (Re-)elected: ffff00ff / ffff80ff
Indep takeover: ffff00ff
Indep retired: ffff8080
Indep up for election: 00b400ff
I plan on using this format for all U.S. election maps that I'm converting to .svg. To make a suggestion, or have a question, go to my talk page.