You can permanently change the color of your text that YOU see by pressing Alt-K or going to View > Colors and changing "Own Text" and any other text that you want.
If you want to permanently change the color of text you send to the channel that OTHERS see, you need to use a script. Keep in mind, however, that many channels do not appreciate people talking in color all of the time and many bot scripts (trivia, games, etc) don't work if you type their commands/answers in color.
