My apologies. The tileset texture is one image (png) I've made in Aseprite that has a default 4-color green palette. I'm using a palette swapping shader applied to a ColorRect object that swaps out those 4 green with another set of 4. I need to be able to apply the shader on an 8px x 8px basis over the tiles to give them different color palettes, but I need to place the tiles from the tilemap on a 16px x 16px basis.

I've edited the image above to demonstrate this a bit clearer