This snippet will allow you to change the color of the Design selector and the Create Site button on your reseller portal.
<style>
#ds_root .thumbdiv.thumbselect, .reg-content-home .layout.selected, .reg-submit, #largeviewcaption #largeviewdesignselect a { background-color: #279A32; }
.reg a:link, .reg a:visited, .reg a:hover { color: #279A32; }
</style>
*Update #279A32 with your own custom color code.
NOTE: This snippet is provided as is, with no express or implied warranty for accuracy or accessibility.