Hi...Can someone help with this please. I have a graphic which is yellow. Created in Gimp. Every time I want to changed the colour I select the color I want to replace the yellow with and bucket fill with the replacement colour. I have noticed though that when I increase zoom by enough it becomes apparent that the bucket fill is leaving pixels at the edges of the graphic Im changing the colour of in the original colour. I cant figure out why. When I select by colour it actually selects the area and leaves the ants marching a couple of pixels back from the graphic edge. Grow dosn't help.

Never mind ...solved it

Because at the edge the pixels have intermediate colors, and these are necessary to keep smooth edges. So if you select too much you replace these by your new color and get a jagged edge, and if you don't they don't get replaced and you have faint edge with the previous color.

The actual solution:

1) do a "color erase": pixels of the color become completely transparent, and the pixels at the edge become partially transparent. Two ways to achieve this: Color>Color to alpha, or bucket-fill in "Color erase" mode.
2) fill the void: fully paint the fully transparent pixels, and paint just enough the partially opaque pixels. Again: two ways: add a new layer under your layer, and bucket-fill with the new color, then merge down, or bucket-fill your layer with the new color using the "Behind" mode. In that mode, paint is applied only on transparency, so that all pixels becomes fully opaque (but those that were already fully opaque remain unchanged).