I spent a bit over an hour changing one element at a time to figure all this stuff out. If you're looking at the main forum page, within an individual forum from top to bottom the rows are:
Table Ledger (.tableLedger)
Search Sub-ledger (.tableSubLedger)
Tables (.tableRow)
If my scanner was working, I'd offer to send you what I have.
Print a few pages from the forums - eg. the main page and one with a post, then change one element of the default_style.css to a lurid colour, upload and refresh, then mark it on the printout. Repeat with the others. It's tedious but after an hour you have a map which tells you what every element of the CSS file refers to.
Then it's a breeze to customise the colour scheme.