the trick with product options that effect price is to not have the add to cart button create the select list, don't check the up-dateable option for the color.
if you look at the eCart options tutorial, it is broken down into 2 sections, options that don't effect price and options that do effect price.
in the tutorial, the color section does not effect price, and the size section does.
the size select list is created manually, a lookup recordset is created to lookup the price increment and size name, in the add to cart button behavior, the size and price increment columns are bound to the corresponding columns from the lookup recordset.
if the color will effect the price, it needs to be configured using the lookup recordset.