Right now, you can only change the background for the entire board, and you can't set background colors for individual cards.
However, there's a Chrome extension that you might want to look into, that does allow for that: https://chrome.google.com/webstore/detail/card-colors-for-trello/nodlpencjjlohojddhflnahnfpfanbjm?hl...
There doesn't look to be a way to turn on looking at the text of the labels to display, you can turn on color blind mode on your account if you don't want to just use the colors. This article has some helpful tips for how to best use labels.
You can also filter cards if you would like to only see certain cards at a time.
You might want to email email@example.com to ask about possibly turning on the ability in the future to change the color of the card or to display the text of a label!
Hopefully that helps!