Tile background isn't transparent

[guy_who_makes_rpg]

I was loading my map into pygame with pytmx, and then this bridge suddenly has a background!

In the map editor:
so why is it greyish-green?

[eishiya]

When you created the tileset with the bridge, did you need to set a transparency colour? Perhaps you haven’t done the equivalent in Pygame, causing the background colour to appear in-game.