Hi @rosaline, as you saw the problem is related with the number of colors (special layer blending modes can cause a multiplication of colors too, so exporting an .ase to a .gif can be tricky in these cases).
If you need some answer about your specific .ase file and you cannot share it in this forum, you can send me it privately to support@aseprite.org and discuss there what is wrong with your specific file. (Include the version of Aseprite that you are using too)