You are correct sir, all of us suppliers have our alloys down and have been tested for the best results. Some may vary in color slightly and perform slightly different but all are designed to provide the reddest color with out jeopardizing workability.
Red gold (especially 18kt red/pink) can be a tremendous challenge to alloy and even cast due to the high copper content and the forming of copper oxides. Quenching, soldering & fabricating require some tweaking in process when compared to yellow gold.
Ken Babayan
David H Fell & Co. Inc.