From the documentation:
The tool options also affect the way transparency is handled.
The amount of fill depends on what Fill Threshold you have specified. The fill threshold determines how far the fill will spread (similar to the way in which the magic wand works). The fill starts at the point where you click and spreads outward until the color or alpha value becomes “too different”.
When you fill objects in a transparent layer (such as letters in a text layer) with a different color than before, you may find that a border of the old color still surrounds the objects. This is due to a low fill-threshold in the Bucket Fill options dialog. With a low threshold, the bucket tool won't fill semi-transparent pixels, and they will stand out against the fill because they have kept their original color.
If you want to fill areas that are totally transparent, you have to make sure that the “Lock” option (in the Layers dialog) is unchecked. If this option is checked, only the non-transparent parts of the layer will be filled.
I have run into this problem of filling transparencies etc, hopefully this will make more sense to me after researching and playing with this tool.
The sun is shining, the dog is glancing at her leash, this will have to wait for cloudy weather!
Comment deleted by an Administrator
There was limited amount of good information out there in using the Bucket Fill Tool. As we go along and see it being used in different ways we will update this post. Feel free to add any useful information about the tool here. In the mean time playing with the tool may bring some insight that I will share here.
(The reply above this was deleted due to my abundant typos! ;-)
I've found the Bucket Fill tool to be fairly straight forward and easy to use for the limited projects I've attempted so far. I cheated and watched the rest of that tutorial on the Gradiant Tool too. Some wayyyyyyyy cool things to do with that baby...
Yes the blend tool is cool and we are just now studying it.