I was thinking (not saying anyone else was, I'm a total beginner) that it was a good idea to have the lines only show on a layer. And to remove colour (in this case, remove the white). I can do that with Black & Alpha (or maybe I used Colour and Alpha, not sure which I used). So on one layer just the black lines show, in-between lines is no colour, so on a physical level, it's like a transparancy with the lines drawn on. Of course, you see the chequeres on the layer
Not sure what advantage doing that has. :c) Because bucket-fill won't work, except on a layer with the lines. Which in my case destroys the "transparancy" that I have just created.
From what I've done, making this "transparancy", I have to draw in the colours on the background with a mouse using the transparancy (layer) to guide. Cannot use bucket-fill.
As regarding using bucket-fill, if the lines are strong then of course that reduces the need to erase (or do little fill-ins to complete the fill). So, perhaps then the first focus is getting the lines strong. And if that is the key, if it's not unduly onerous, then one is going to use the bucket-fill. So, my transparancy layer I've made, has likely no value. :c) Unless it's quicker to "manually"colour in the backround, using the transparancy as a guide rather than "fix" the lines.
Bucket-fill, or not to bucket-fill - that is the question. :c)