you need to use a tool like MySQL Query Browser, to add new entries into the StyleVariation table.
StyleVariation has FK_Style references, which refer to the styles defined in the FK_Style table.
You need to also get the PK_Skin # for your skin from the Skin table.
and if you look in stylevariation, you'll see entries in there for the different styles, and FK_Skin entries for each of these styles you wish to override. The only entries that need explanation, are the different color columns, to get these values, get the web color for what you're wanting to use, and use a calculator to convert it to decimal. You then get an integer you can put into those fields.
0 would be black, and since the integer is signed, and 16777215 or -1 would be white (because negative numbers go backwards).