As someone in their mid-30s, I can't actually even see the bright font on the mods, as there isn't enough contrast for my eyes to differentiate between the two.
While I understand the worry of brown font on brightly coloured mod keys, I don't think it would look as out of place as believed - I'm a huge fan of Novelkey's PBT Notion set, which worked around the potential issue by offering both accent AND plain-coloured keys but with a consistent font colour throughout the base kit.

For those who wanted Text & Icon modifiers, I'd be willing to forego buying novelties for an all-icon mod kit, especially if it included icon options for the nav cluster.
Sadly no manufacturer is currently nailing reverse dye-sublimation, and I think you'd have much less hesitancy from potential buyers if you were able to avoid it in the base kit.