I'll suggest to the OP to put Paint.NET in the list of not recommended until I find if it is possible to save the pictures in a way that doesn't screw the color code or a way to fix the palette within the program (in case it is that which I doubt).
I've checked better; paint.net is really good, only problem it does not handle palette files in .pal format, like openxcom ones > = (
In the meantime I've been tackling mtpaint (which seems good but I haven't got the skills yet) and graphics gale, which has a free edition and was recommended in a pixel artist web for beginners.
Good news, as for editors
GraphicsGale as of 28 june, 2017 is gone freeware, it has also a protable win version too. Also
Pixel edit seems to be nice, the older verisons are free, but file opening is done by selecting import inage, and sa, export. Same as palette, in colors menu, but it is gotten from existing images, no directly .pal file loading. A windows only useful too is
rotsprite, to resize and rotate sprites.
Aside from the recent fork of Gimp,
Glimpse (basically providin' some interface adjustments) after some other search i found a very excellent alternative to
Aseprite:
LibreSprite! Avaiable for win (installer), linux (as portable AppImage) and macos, it has nearly all the function of the paretn program, a screenshot is attched as well
Here is a quick showoff video too,
here. There is a video demonstration - about one hour (!!) -
here.
Pixelorama is a nice editor which can even make animations,and in the 0.8 version
added support for palette in .pal format, another choice might be
mypaint Also, a good alternative to win-only irfanview might be
xnview MP from
xnsoft, it has also a
wiki.
Oh, also this thread need to be moved in the
Tool board