Whenever I can use color I will do the Title in color. Most people will not read the email unless there is something in the Title that gets their attention. I also found that when I am adding a list of benefits within an email, I like to add color to the specifics of each point. For example, if the benefit is 'use the mailer to promote your main business', I will do color for the specific benefit and bold text. I find that people will glance at the title, maybe scan the email, and only click through if something stands out that they believe they need. I use low, non-glaring colors, usually red like above, or green or blue. For me, glaring color is a turn-off. I don't like bright yellow highlighting.