It’s defined in the css file, and have you look at the colors that are already available http://demo.styledthemes.com/lavish/colors/ you can use all this color to the buttons too.
Let us know if you still don’t find the color that you want so we could provide you the custom css code.
I don’t see references to these colors in the CSS. I was hoping I could either add a custom color to the group or change the hex color of an existing one so it would match my branding better. I just can’t see where those colors are defined to make the changes. (I’d like a color that is: #4082cd) You have some that are close, just not exact.