Hello,
(sorry, very late reply)
I can still reproduce with mplayer in unstable (svn38446), however I
suspect that it's another case where the expected behavior is turned off
by default but can be activated with an option.
For instance
mplayer -ass myvideo.mp4
correctly display lines like
<font color="cyan">Not really.</font>
defined in myvideo.srt
The default color for subtitles lines where
there is no <font color="cyan"> becomes yellow.
The default (white) color can be restored with
mplayer -ass -ass-color ffffff00 myvideo.mp4
Regards,
Lorenzo