if you run your nail over the pale pink to dark pink edge, can you feel the slightest 'raise' in the dark pink, over the light pink.
I'm attaching a picture of a piece that might be difficult to explain what I mean, but this piece has three layers, clear, white and dark blue. However because the dark blue has been cut back in parts to a very thin layer over the white, it appears much paler (though not as different as yours does) blue with the original dark blue layer just left in parts. The dark blue layer is the same layer as the polished layer left around the base. It's just been cut away to a thinner layer so shows as pale blue giving the effect of three colour glass.
Hopefully you can see on the bottom photo, that some areas of the vines appear to be very dark blue and others a much paler blue and then some white showing as well. All that blue is the same 'layer' as the dark blue polished border at the bottom.
Your dark pink that's left as outlines may appear to have a greater 'change' in colour between the pale and dark pink because of the way it's been cut, i.e. quite definite outlines.
As per Peter's post