* Replace `culori` with simple color parser
* Use space-separated color syntax
* Update default color values to use space-separated syntax
* Update separator regex
* Fix tests
* add tests for the new `color` util
Also slightly modified the `color` util itself to take `transparent`
into account and also format every value as a string for consistency.
Co-authored-by: Robin Malfait <malfait.robin@gmail.com>