Yes, you can find some yellow between the bill and forehead of RBW, but of course with all that red on the head, it is barely noticeable most of the time. The ones that I have seen all looked red, but probably had I looked more closely, I would have noticed it.
With GFW (I haven't seen this species, but I have a Peterson guide in front of me, so i.e. very reliable book), there is a lot less red. I shall describe both male and female to make this easier, because you may have seen a female RBW:
Whilst the male RBW has a red topped head all the way, the female RBW has a small stripe of gold above the beak, followed by a chunk of orange, and then a faint bit of more gold. Then there is a head cap of grey, ending at the back of the head in bright red.
With the male GFW, there is a large chunk of gold at the bill, followed by a bit of grey, then a red cap, more grey, and some firy orange. The female GFW has a gold tuft, then completely grey head ending in a gold back to the head.
On these notes, I would say you were looking at a female RBW.