VCB,
A dull gray is fine, and is what I noticed on every other Bushmaster except mine. Usually a bit of it would extend out beyond the crown in an uneven fashion around the tip of the barrel.
On mine, the Black phosphate coating was all that covered the crown, with no visible sign of gray at all, and down into the barrel for a few millimeters (had a very bright light I shined down into the barrel to see this) before the dull gray of chrome lining slowly started to take over.
Edited to add, though some chrome lined barrels I own have a shiny polished look (my SAR-1 does), I also have a chrome lined Springfield M1-A which has the same dull gray as the Bushmaster. Don't know why some chrome lined barrels are gray, and others are shinier and more polished in appearance, and which is better.