I don't like the white cards on the light grey lists. I would like a way to make them stand out more. The lables just put a small strip of color. Can I change the color of the cards, the lists or even the text?
Unfortunately not, coloured backgrounds are currently under consideration as a new feature on the Trello development board, go to Trello dev board and place you vote.
beautify claims to do this
It's a workaround, a Chrome extension that enables options like this. Not perfect, but it might get the job done.
There's also a stylish script, but it's out of date.
SteB's answer is also worth checking out, and be sure to submit a feature request.