It might just be his iridescence, can you get a close up picture for me?
Many Betta's have two "stripes" of scales on their head, one is just before the gills, it's right on the plate covering and another where the plate goes out when he flares.
Here is one of my girls but you see she's got two red stripes on her face? Those get even more red when she's ticked off at someone but they are very normal and it depends on the Betta's color as to what those stripes will be.
Here's my boy Remmy who has blue stripes, although they aren't very bright since he wasn't mad ahah
So does it look like that sort of? Just golden in color?