That's absolutely awesome!
Maybe the red in the middle not so dark. And maybe the borders around the mountains a bit weaker, so that they melt with the background more.
That knocks out MSX and Amiga! I like the saturated colors. Great work.
Good is that it doen't look bleached out like lots of GFX on c64 or 16-32 bit.
Really hope you will release it one day!!!