There are 3 yellow face mutations: Type 1, type 2 & golden face. The type 1 is a pale yellow, the golden face is very bright yellow & the type 2 is in between. The best way to identify the different types is by the way the yellow spreads into the body colour. The 3 mutations are unrelated to each other and they are all dominant.
There is quite a bit of disagreement about how yellow face mutations should be described but this makes no difference when working out their inheritance. Some people are adamant that the way they describe them is right but nothing has been properly proven
Like any other dominant mutation more than one type of yellow face can appear on the same bird but you probably wouldn't be able to tell visually if a bird had 2 mutations