Twitter just released Twitter for Mac on the Mac App Store, as the successor of Tweetie. Overall it's a good improvement but there's a big accessibility fail:
On the left, the Tweetie menu. On the right, the Twitter for Mac menu. I'm not exactly visually impaired by the normal definition, but I just can't see the window controls (basically black on black), the tools icon at the bottom (can you see the little bird? I missed it the first time I launched the app), and barely the other dark grey icons on black in the navigation column. In the same vein, look at the ‘84’ figure in the box below, another overuse of dark gray on black background:
(Note: these images look more contrasted once converted to PNG and published here, the contrast of the running application is really much, much worse on my screen.)
Let's hope Twitter fixes that quickly, I guess it's going to be the biggest gripe about Twitter for Mac (apart from the usual old-timers complaints about the new retweet feature, which I like).