Welcome to our forum.
Your dealer may have to get spas in truckloads and warehouse them, and as a result, it may cost him more to get a special order. Also, these special orders take the approval of our regional rep - I can't simply punch in an order for a green spa with brown siding - the computer doesn't allow it.
Being the reasonable accomodating dealer you seem to be, do you ask for an additional non-refundable deposit for a special order like that?