This package contains a few simple colour conversion routines. For example, it's possible to convert RGB to HSL.
Calculating complementary colours is also part of the offering.
If you want to contribute, have a look at the Issues. Some issues are labeled 'Good first issue'. They are the low-hanging fruit.
If you create a PR, also add your GitHub username to the list of contributors in the file contributors.txt.
It's a bit of recognition for your work.