UX Power Tools started out as a subscription offering. It has now shifted and become a single-purchase kit, currently priced at $32.
“Devs don’t start projects from scratch. Neither should designers. A comprehensive style guide makes for a smooth design process, and a simple hand-off to developers. Our style guides are meticulously designed in Sketch using Layer Styles, Text Styles, and Symbols, so updating dozens of components takes seconds, not days…”
Here’s a video demonstrating color customization. Visit their website for a full overview including other videos.