The new diff colors have been temporarily reverted. Trevor and Timo plan to spend some time looking into the subject. See: http://www.mediawiki.org/wiki/Special:Code/MediaWiki/112750
So we are back again to bike shedding the diff colors :-)
The revert reopens bug 11374 which is about red text on green background. Fix by MaxSem, in r94429, was to make that text black with a different background.
https://bugzilla.wikimedia.org/11374 https://www.mediawiki.org/wiki/Special:Code/MediaWiki/94429
Can we at least put that fix back?
As for the diff colors, we had a long discussion on r105280 as well as on IRC. It would have been great to ask around before reverting that change, I am not sure it was that urgent. Anyway, can you please poke Brandon Harris about it? He explained the choice of colors on r106884:
https://www.mediawiki.org/wiki/Special:Code/MediaWiki/106884#c28165
The long discussion thread about having green on left or right side. You can probably skip that read. https://www.mediawiki.org/wiki/Special:Code/MediaWiki/105280