Remove funky colors from home screen

This commit removes the neon purple and green colors from the Home
screen. Yes, we had grown to love them. But it's time to let go.

This commit re-implements the whats-fresh-mobile branch of the same
name, however I felt it was easier to just delete these 10 lines than
cherry-pick those changes across two projects.
Merge pull request #4 from osu-cass/feature-3936-remove-funky-colors-from-home-screen

Remove funky colors from home screen