The last of orange, brown, green, grey, black, white, blue, teal, cyan, red, pink, magenta, violet, purple, gold or yellow in the backdrop's name is blue; with none of these words in its name, its centre colour is blue.
In Giftroll, this comes up 1 in 6 a roll. It's one of 9 badges in its family, and a roll counts at most one of them.
A gift a day, free, no account needed.