When you say how to change "the color on my site", what part of the site are you referring to?
To change the font color, you would use the "color" property in whichever tag you want to change. In Lesson 10 bubble 9, look in the style.css file and you'll see they use this to change everything in the h1 tag to a red color...
To change the color of the background, use the "background-color" property. Here's some documentation: https://www.w3schools.com/cssref/pr_background-color.asp
You can put this in whichever tag/selector you prefer - assuming you want to change the background of the entire page, you would use the "body" selector, like so:
But you can also change the background of specific elements only, like doing the following, which would set the background of the h1 stuff as red:
Hope that answers your question.