Sitecore: Editing font and font color of a slide title

I have a Carousel on a page with some slides. The author can edit the slide's content in the experience editor. i.e. He can change the text and the background image. However, he cannot change the font color through the editor. So the default font-color in the css class, applied to the title field is white. If the author uses an image with a white background, the text is barely visible. How could I allow the author to change the font color in the experience editor for the slide's title field? Maybe allow him to choose from a variant of the title field with a different css class? Except, I don't know how to create a variant for the title field.

You have few options here:

1. Edit the text using Rich Text field edit fame buttons: Rendering Variants are using default Sitecore field renderers so those edit frame buttons come from Sitecore - we are not customizing those.
2. Change style of the Page Content which is by default in each Carousel slide. In that way, you can also easily change font colour. You can also use edit frame button but this time on the Carousel itself:
3. Change style of the whole Carousel - the same approach as above but not for the Page Content but for whole Carousel.

Carousel Slide by default contains Page Content inside which is using variant configured to display fields from carousel slide. You can of course easily change the variant and display whatever you want. If you need more information's about rendering variants take a look here