The texture work is being done primarily in Gimp, although I do sometimes generate nifty procedural textures in Blender to add to layering complexity when I make these planet textures. I also sometimes work on land mask outlines in Inkscape to keep them scalable until I know what resolution I will want for the texture.
All of my rendering, of course, is with Blender. 
I’m pretty happy with this base layer. I might next work on a cloud texture that will look good with the land pattern on the globe.
-waystar