Correct; presumably it's for the month of June (Gay Pride). But it is particularly appropriate in light of today's events.
actually it's context-sensitive. If you start typing "gay" into the search box on top, the rainbow styling comes on. If you type in something "gay" that has a more negative association, it doesn't. Try entering "gay love" and then "gay hate" or "gay rights" and then "gay bashing".
Hmm, gee, it doesn't do that for me (although I have google auto-complete turned on)...
"hrc" will also do it
I thought that stood for "Hillary Rodham Clinton" at first, and thought they were being a bit presumptuous there!
(I know she's a supporter of gay rights, but it would be a big leap to translate that into rainbows showing on her google results page)
As will "sf pride", a reference to the San Francisco Pride parade and celebration, which happens to be this weekend.