Why are we limited in our choices of Terrain paint?

Dear developers of Dungeon Alchemist, i really like the game so far.
Aspecialy the newest update for building roofs is in my opinion very great !

But one thing really striks me as odd.

How come im bond to a surtan palet of Terrain paint depending on the Type of terrain i've choicen for the whole project.
This way its inpossbole for me to build transissions or experiment with other kinds of backgrounds.

Like to hear from you greetings,

D&Diebels