In V1, there are two approaches I’ve found to be fairly straightforward.  The first is to use a either a Salesforce (preferred) or Skuid formula field to set a Class name based on some criteria.  Then you can use merge syntax in either the class setting in the page composer or in template html markup.  If you are using a component like a deck that has model context, you should use the Model merge syntax like class=“{{className}}”.  We use this approach with color coding tasks based on their status.  

If you simply want to swap out the color, you can setup the color code in the formula field and use a style attribute with the merge syntax to set the color, like Peter indicated.

Here are a couple other posts with more detail on this:

https://community.skuid.com/t/conditional-css-deck

https://community.skuid.com/t/color-picklist-value-based-on-status

I have word that Spark will be getting conditional styling, which I’m very excited about.