You can't do overrides with S2; what you can use is CSS. All the things you want to do are possible, but you'll have to write a small style sheet to specify each thing you want to change and paste that into the big CSS box at the bottom of the Custom Options tab.
If you're not familiar with CSS at all, and don't want to learn it this week, you might want to check out nameless_layout and load up one of the S2 themes that has a built in dialogue to customize colors, like Smooth Sailing or Flexible Squares. You will have to upgrade to a paid account for that, since it involves pasting in a new theme layer.