Well, that's odd. But not all that troublesome. Our sister site
https://ux.stackexchange.com/ use no icons whatsoever, but make the Ask action look like a button. Here, we use a different color to make the ask action stand out.
But I agree with you, it should have an icon to emphasize its use.
(using an answer to be able to post a screen)
Currently using win 7 + ie 11 RTM. I don't see the aforementioned bug. Are you using win8?
Also, any idea why the update version is different?? Maybe you upgraded from the pre-release version? Or it is me using an old version (a good reason to NOT upgrade, then)?
I think the same rainbows appear on the SharePoint SE, just with a different background color. Additionally, the colors have been there on SE's side for a long time. Therefore this change is likely just for unifying the layouts of the SP.SE sites.