Planeswalker colors and colorless walker inconsistencies.

Emissary

So using a card like Fire of Invention with Karn gives you reduced cost equal to gem count of your planewalker colors, but only counts loyalty gems. However a card like Ulamog, the ceaseless hunger, converts each gem of an opponents's primary colors (same thing as planeswalker colors) to void gems and will convert the whole field to void gems if against a colorless planeswalker. So one of these two cards is bugged since they have the same target but vastly different outcomes.