All that stuff blur did adds a nice amount of colour variation. Since that stuff is castleish, torches would also be a good way to add some red. I also think that part of the tileset could use roofs, but I think blur will work on that part himself. Trees would also fit well in this tileset, which would add a bit of brown.

I also think that this tileset would make for a good swamp themed level. Maybe add some water tiles? Dark blue would fit best, I think.