Numbers usually mean colour intensity. Have a read to get a better idea behind it
Also, you may check this plugin - https://www.figma.com/community/plugin/1297031341980383999/source-foundation
There is a playground file with design examples where you can see the system described in the article and how it works with real designs. Plus there is a comprehensive guide on how to use colours.
Feel free to bring questions, will be happy to elaborate