I owe a thank you to @Cerise for sparking interest in this idea last week. ubuntu-mate-colours is now shaping up quite well, but still has areas for improvement.
If anyone would like to give it a test run:
sudo add-apt-repository ppa:lah7/ubuntu-mate-colours
sudo apt install ubuntu-mate-colours-all // or -aqua, -blue, -red, etc
See the README for colours or if you'd like to create your own:
Any issues, please report to the Issues page -- there's also the opportunity to help out with contributions since I'll be shifting my focus on some other projects for now ( 
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Since we lacked SVGs as discussed previously, I did accomplish the colour change using imagemagick - which seems to have turned out alright 