Here’s the same picture made with two similar but different color pallets. On pallet is good, the other bad. The first image is a small version of the good picture.
Here’s a tip for changing pallet in LibreSprite: In the toolbar menu choose select → color range, then choose one of the colors you want to replace and click ok. It will select all pixels of that color and you can draw over them with a new color.
If there is a better way to do that I’d be interested to know what it is.