You may have already learned of this but if not; ... It would be expensive but you would have an experts opinion. One caution, as you have probably figured out from these posts that even experts sometimes disagree. My suggestion: on
ebay under US stamps search for "STAMP EXPERTIZATION SERVICE". Mr Weiss offers a service to identify a stamp as genuine and as I understand it, he gives the color name when necessary or if you ask him. price is $20.00 plus shipping. He is well respected and is much less expensive than other expertizers.