Add colors to gif palete gimp

Question

When I open a GIF file in gimp, I find it very hard to add more colours then those that are already contained in GIF palette. When I draw with different colours, GIMP is trying to use the colour from palette most approximate to the colour I'm drawing. (may result in red instead of black)
This problem persist even if I save the imported GIF as XCF file (even if I create new layers in it). How do I make gimp ignore the palette? The only solution was saving (exporting) the file as some non-palete image as BMP and then importing it again.

Example

:

After flood fill (black)

Answer 1

When you are working on an indexed image, GIMP uses only the colors contained in the image palette, i.e. the set of colors allowed for that image (max 256 for GIF files).

GIF files are indexed images, and even XCF files could be indexed, so in order to add new colors you can either change the image mode to RGB (this allows you to use up to 16 Millions of colors and, if needed, you can export as a GIF after your editing - this operation "squeezes" used colors in a 256 color palette), or edit the palette of the image (changing existing colors) through the colormap dialog.