Jekyll: including SASS color variables

I'm not quite sure how to word this out, but I am trying to use sass variables in my Jekyll site. Specifically, I'm trying to use the variable, "$color__background-body". When I set that as my background color, I get this error message: "Error: Undefined variable: "$color__background-body". on line 6 Error: Run Jekyll build --trace for more information."

and my variables wont show up on "my _site/css/main.css". Is it just not possible to use color variables for Jekyll?