We produce our keycaps with the original Cherry tools.
During the time when the keycaps and tools were developed there was no interest in backlighting at all.
Besides the material, the opacity depends on the used grid. You can see this grid if you turn the keycap.
For the manufacturing of the different legends we use different grids. Some of them have more openings than others.
That's why there may be differences in the translucence.
In general we can't guarantee an opacity of 100%, due to the many variables (colors, grid, used LEDs).
Nevertheless, we have assumed this problem and we could improve the opacity by changing the material supplier in the recent weeks and months.
We made some series of experiments and the opacity of the new material is much better than the old ones.
Due to the above mentioned factors we unfortunately can't guarantee a 100% opacity and compatibility for backlit keyboards.