Take a look at your phone. Open up the Google Experience launcher (the default one on Nexus devices), or if you're using Android 5.0 or later, tap the "Recents" button. Alternately, add the good old-fashioned Google search bar widget to your third-party homescreen. Now, take a look at the left side of the bar: do you see a Google logo? Is it grey, so as not to call attention to itself, or does it look like a spoonful of Froot Loops, like the Google web logo?
We've been getting tips from users who see the latter, colorful logo on Android for the last couple of days. The switch seems to be entirely server-side, as multiple readers have seen the change while running different versions of the Google Play Services app. It's possible that Google is performing some A/B testing, enabling the multicolored logo for a few users just to see how they react. Apparently their reaction is to tell us, and of course, our reaction is to tell you. You're welcome.
Here's the current grey logo, just for the sake of comparison.
The change is aesthetic, and therefore subjective, but I have to say I prefer the more subtle grey logo. The Recents page in particular is already a busy jumble of colors and formats, so why add one more distracting element? Anyway, right now it seems to be appearing for a very small subset of users. We'll see if it expands over the next few weeks.