From version 1.7 onwards two new parameters are available: color and theme.
Check the documentation for available values:
- color: http://code.google.com/intl/en/apis/youtube/player_parameters.html#color
- theme: http://code.google.com/intl/en/apis/youtube/player_parameters.html#theme
An example:
Shortcode parameters used:
url=WeLjzzTLT08 color=white theme=light