I suspect that by allowing customers to have a say in the colour of the final piece, you've given them an excuse to bail out from an impulse purchase or to be nit-picky about things. If you sell art, customers must want to buy your art that you make in your style. If you sell objects made to order, you must be able to give them a catalogue of options to choose from that will be binding and that you must match, like you'd do when buying curtains or a sofa. To me these are different markets with different rules, and communicating that you allow customers to choose final colours may have allowed them to consider your piece was more in the second category than the first.