added a comment - - edited
Indeed, this change was one for the better, and I hate to be a pain in our bunghole but: I still think the subtabs need work to a similar direction.
That is, it is not quite clear visually that there are subtabs in the first place. They do not have the visual appearance of tabs. This becomes problematic in otherwise busy UI's, such as the new Quiz UI (MDL-17284). While the eye scans the page I suspect it is easy to dismiss the grey gradient strip below the primary tab bar as just a visual element.
I propose a solution such as that in wordpress: have contrasting colors in the second row of tabs, i.e. as the first row of tabs has dark text on a light background, make the second row of tabs have bright-colored text on a dark background.
See http://moodle.org/mod/forum/discuss.php?d=72828#p326202 for an example.
The thing that makes this issue even worse is that the default theme does this halfway already: That is, the second row indeed is quite dark already, but the text is also dark, making the text harder to notice, even more so in busy UI's.
The minimal help to this issue would be to at least highlight the active tab by removing the dark color behind that active element, as demonstrated by the wordpress example.
Improvement
Closed
Minor
OK done. I hope this is uncontroversial. It seemed over the top to post a patch and ask for comments before committing.