I've seen early BBA appear like this..I've also seen Cladophora Algae appear like this
typically BBA is black.. in my QT I 've seen this recently which started out light in color (lt brn nearly translucent)
in my 75 discus tank it appears as Cladophora..light tan/translucent..I did a black out in the75 which cleared the problem.
I then transformed the discus tank into a low tech tank and it's been goine ever since then.