If you changed Variant Dropdown format to Button, and now you want to use custom color on each buttons. You can use this code to Website > Website Tools > Custom CSS.
In this case, Variant Name is Color
label[for*="Color-BLACK"] {
background-color: #000 !important;
color: #fff !important
}
label[for*="Color-BLUE"] {
background-color: #5dc1f3 !important;
color: #fff !important
}
label[for*="Color-RED"] {
background-color: red !important;
color: #fff !important
}
label[for*="Color-ORANGE"] {
background-color: orange !important;
color: #fff !important
}
label[for*="Color-GREEN"] {
background-color: green !important;
color: #fff !important
}
label[for*="Color-CHAMPAGNE"] {
background-color: #cdbcaf !important
}