Improve Formula for Display Colours (#2375)
Improve Formula for Display Colours (#2375)

* Update luminance formula

Following #2315 this updates the formula for computing the luminance
of a brand colour and selecting the appropriate colour class.

--

Co-Authored-By: Peter Noble <5e2141330464ca04ae3eb04147f3d83fee03b39b@users.noreply.github.com>

* Update luminance threshold from 210 to 160


danleech/simpleicons.org,simple-icons/simple-icons,simple-icons/simple-icons,danleech/simpleicons.org,danleech/simple-icons