After researching lots of companies that make stain for brick I decided to contact Pro Mason for their professional advice. I went with a 4oz sample of antique gray, as suggested, and applied it to my exterior orange brick chimney. It went on nice and easy, has excellent coverage, and dried to a perfect match to my gray vinyl siding! I am currently waiting for the gallon size I ordered to finish the project.
I highly recommend this company for their customer service, shipping, and their quality products.