Color is pretty good for separating things. That’s what your basic pie chart is, isn’t it? You tell the slices apart by color. With enough color contrast, you might be OK, but you might be even better off (particularly where accessibility is concerned) using patterns, or a combination.
You can use the patterns.css file that contains all the current patterns. That will only work for non-SVG elements.
You can use individual patterns, but copying them from the sample pages. CSS class definitions can be found here and SVG pattern defs can be found here
You can add your own patterns or modify mine! The conversion process from SVG document to pattern is very tedious. The purpose of the pattern fills toolchain is to simplify this process. You can clone the repo, run npm install and grunt dev to get a local server going. After that, any changes or additions to the src/patterns/**/* files will be automatically picked up and will re-render the CSS file and the sample pages. If you make new patterns, send them over in a pull request!
Here’s me applying them to SVG elements (but could just as easily be applied to HTML elements):