FOSS gamedev and creative worlds

Hey guys, I'm trying to make a texture for something. In Gimp, I'll select Colors/Color to Alpha. It shows up in Gimp with the alpha transparency (the black and gray like grid), however in game my item shows up with a white background. Any help?

Alpha is not supported in any regular blocks or items in Minetest, but it does seem to work in limited circumstances (i.e. the old 2D players, possibly other entities, but I've not tried that yet).

So how do I add transparency in gimp?

Add alpha-channel in the layers window and change tool transparency before drawing.
Alternatively you can set transparency to a rubber tool and "erase" some of opaque-ness.

Make sure it's completely transparent. Minetest will draw it as opaque if there's a slight bit of color.