I think you have "hit the nail on the head", Christine - I think you are correct.
Looking in particular at my vaseline ''Fische'' bowl, I can understand how it appears to be slightly patchy in places. The exterior is matted (acid treated) and the interior is shiny - this provides visual depth and contrast to the moulded fish design. However, it also gives the impression (in one or two very small streaks / patches) where the exterior matt finish is absent, that the colour is slightly different.
Of course - this is vaseline green glass - so it cannot be an applied colour. Uranium as a colorant must be added to the glass batch. The glass is self-coloured, so any effect on the surface that suggests the colour is applied / superficial, is a visual trick.
That's how it seems to me, on studying my examples, for my glass. I just can't be sure for Pamela's pieces, as of course, it is necessary to handle these items and actually see them.
Glen