The gold thread beautifully embroidered around the letter "A" on Hester's chest could also symbolize something holy. It could represent a golden halo of sorts that represents Hester's kindness and godly qualities. Hester becomes an asset to the community not only as a wonderful seamstress but as a someone who tends to others despite the community's persecution of her. Her actions are pure and innocent without motive or want of anything. She also keeps Dimmesdale's secret despite her own hardships, a sacrifice that not many would make. The "A" could represent "Angel" and has been interpreted as one of the meanings of the letter. Hester is the most redeeming character in the story; she accepts her responsibility in the affair and tries to live a life that will allow her to earn God's forgiveness. It is also by the grace of God that Pearl is born out of the ugly sin she feels she committed.
I would say that gold along with the color red set Hester Prynne and later Pearl apart from the rest of their Puritan society. Although meant to be worn as a badge of sin, Hester elaborately embroiders the letter "A" with gold thread, which makes it quite beautiful. Also, Hester, a master seamstress, does nothing to hide the beauty of her daughter. Instead, she creates lovely dresses for her fit for the rich. So it seems to me that the color gold along with the color red, which are traditionally seen as royal colors were used to showcase Hester Prynne as a loose and shameful woman, and that Hester in turn used these colors to both showcase her daughter's beauty and at the same time make her the physical manifestation of the letter "A".