Granted it isnt ideal but it IS possible to do editing on Android. At the moment im using a phone because I dont have a comp, and ive gotta say OpenXcom is a great game app to have for it, it really blows away most of the modern game apps.
Grafx2 has an android version and ive been doing minor sprite work. Also QuickEdit has YAML editing capacity, no thread collapsing like Notepad++ but it does syntax.
Ill also mention again the Falco OpenXcom tools website.
Question I have is are there any Online image converters that will convert an image to a specific 8bit palette? Because Grafx2 doesn't have the ability to save/load palettes or convert them. Im not sure if Gimp has an android version but its palette stuff has never been trustworthy.