There isn't a tk2dSprite for each tile, everything is merged into the larger partition system. You could, I suppose change the tilemap colors so they aren't interpolated - that way, the tiles would use a solid color each. tk2dTileMapMeshBuilder.cs, BuildForChunk is where this happens, look for
Color color = Color.Lerp(
Color.Lerp(tileColorx0y0, tileColorx1y0, tileColorX),
Color.Lerp(tileColorx0y1, tileColorx1y1, tileColorX),
tileColorY);
You can also change it so painting a tile down will paint a color down at those positions as well, if you wanted to take it further.