This is one case where small is not a great advantage. As downloaded, only 316x247 pix. I would not even think about bucket fill. Make plenty layers and paint under the original.
First of all give the original transparency. Layer -> Transparency -> Add Alpha Channel Then remove the white, leaving the outline. Colors -> Color to Alpha (white is the default)
Then plenty of layers, one for each colour / area and paint in. The order of the layers does matter, a higher layer masks a lower layer, so think about it.
The only snag is a white? stone, I had to make this on its own from the original, erase and adjust before adding right at the top of the stack. I think a bit of texture is best - up to you.
All-in-all not as straight forward as you might expect.
example attached, check the layers.
First of all give the original transparency. Layer -> Transparency -> Add Alpha Channel Then remove the white, leaving the outline. Colors -> Color to Alpha (white is the default)
Then plenty of layers, one for each colour / area and paint in. The order of the layers does matter, a higher layer masks a lower layer, so think about it.
The only snag is a white? stone, I had to make this on its own from the original, erase and adjust before adding right at the top of the stack. I think a bit of texture is best - up to you.
All-in-all not as straight forward as you might expect.
example attached, check the layers.