Apologies for the delayed response; I was digging around old threads on the forum and realized this was never answered.
This might be related to an observation in a more recent forum post:
The color white is a special value. […] It will render the tileset’s original color for meshes.
I wonder if that’s what is going on here. What happens if you set the color from #ffffff to something a tad darker, like #eeeeee? Let me know if that works.
Best,
Janine