When you are validating a value from a select list you will be using the required/not blank/selection made validation. This will ensure that the option the user selects has a value attribute with something in it. You will need to make the value for the 'select color' be "". So this:
<OPTION value="not selected" >Select Color </OPTION>
Should be like this:
<OPTION value="" >Select Color </OPTION>
If you apply the required validation on this field it will fail the validation if the user has this option selected.
For the items that don't have these options you will need to have a hidden form element that has the same name and a value to ensure that the validation does not fail. I hope this clears things up a little, if you have any other questions please let us know.