When I pick my .pal file nothing happens. Is there a log to see what goes wrong? Or some limitations to the .pal file documented somewhere?

I've just checked the file and it seems corrupted, or It's a file format that I don't know. Tried using it on Aseprite too and it didn't recognize it.

Aha, my bad then. First time I've used .pal formatted palettes, I just tried the first online converter I could find.

Fixed a new exporter, (used aesprite) and get this:

___________________________________________
############################################################################################
FATAL ERROR in
action number 1
of Draw Event
for object scp_object_slider:

Push :: Execution Error - Variable Index [0,257] out of range [1,257] - 64.<unknown variable>(100073,257)
at gml_Script_set_palette
############################################################################################
--------------------------------------------------------------------------------------------
stack frame is
gml_Script_set_palette (line -1)
gml_Object_scp_object_slider_Draw_0

Any plans to allow palettes bigger than 256 colors? Mine is 300