The latest addition in the new version of Gmail features list, is colored label announced on Gmail blog. You can now set a different color for each label so you can identify messages easier.
Gmail, Google, Labels, New Features, Featured News
From Gmail blog post: The colored label. Until now the label has been a little inconspicuous creature, subtly suggesting categorical associations in its simple green coat. Oh, we've seen the colored label here and there, its precursors surfacing in various experiments and Greasemonkey scripts; but the label has never before been so brazen, so bold. How will it use its new colors? Will it disguise itself with the chameleon's camouflage or clamor for attention with the monarch butterfly's vivid contrast?
Me? I'm subscribed to a lot of mailing lists: "The Britney Spears Fanboy Club," "Foie Gras Lovers Anonymous," and "UFO Sightings Daily," just to name a few. I get so much mail from my lists, I filter and archive most of it right away but I add labels just in case I need to find it again later. Those labels are my chameleons draped in subtle tones of green and blue. They're there doing their job, but I barely notice them. Every once in a while I get mail that's really important. These emails get my monarch butterfly labels, sporting bright red and yellow. Thanks to colored labels, it's easy to scan my inbox and immediately find all the emails that are really important to me.