I think the GitHub issue #2318 linked to in this post has some pretty clear steps if you want to build a new viz from the ground up:
If you're going to either modify visualizations or build them from scratch I guess you also need some java-script (in particular React) skills, then for other types of graphics d3.js or dc.js understanding as those are libraries Metabase already build on.
If you OTOH are asking specifically about tweaking the styling of the table widget I guess a GitHub pointer would be to look for files called Table<something> in
metabase/frontend/src/metabase/visualizations/components at master · metabase/metabase · GitHub
Maybe also Table layout improvements by tlrobinson · Pull Request #4977 · metabase/metabase · GitHub which got merged in May points to useful files - and reasoning/links to what the Metabase dev team are thinking in this area.
Regarding color options specifically for the table component there is this issue that i personally would love to see implemented! Is that eventually something you are looking to tackle?:
It's not that the Metabase project is lacking any feature requests labeled Visualization/Chart Settings though. Here's the list of issues sorted by number of 
votes: Issues · metabase/metabase · GitHub
Update: phew, overlooked issues marked Visualization, thankfully the two lists has some overlap
But I guess it's easy for people to raise issues, much harder to actually find time to (help) implement stuff.
What are your top pet issues in that list? Maybe there's common ground for a few idiots 
to help each other with actually getting to a point with building stuff?
Hope (some of this) was what you were looking for? 
I'd be happy to continue the dialogue