Single factor yellowface I typically has a very light lemon yellow color to the face.
The body color for a single factor yellowface I should ideally have yellow only on the face with a pure blue or grey body. Some will have a very light spread of yellow, but it is much less than a sf yellowface II or sf goldenface. A light yellow wash is often seen on any areas that are white such as the undersides of the tail.
When this mutation is combined with double factor spangle, albino (creamino) or dark eyed clear a light yellow coloring is usually present on the whole body, with the strongest areas being the face and tail.