The poor man's photoshop

[puggsoy]

Does the transparency issue also exist with PSDs? When making sheets I just keep mine in XCF format (GIMP's equivalent of PSD) to preserve the layers, and then when I'm done I add the background and save as PNG.
If you can open PSDs with transparency, you could work with PSDs to keep transparency while making sheets, then save the end result as PNG.

That had occurred to me while I was writing that post, actually (except that I've never used .PSD format). The only thing is that working with the sheet as one format with transparency, then converting it to .PNG does not keep the transparency. But if I wanted a colored BG, I would've kept it as a .PNG with no layers in the first place (which is what I do most of the time).

Even if you're using a coloured BG (which is required/preferred here anyway), it's good to have transparency in case you want to change the BG, or make some other subtle changes. Also, keeping it in layers (which PSD does but PNG doesn't) allows you to move stuff around and rearrange it if needed.
PSD isn't really that difficult to get used to. If it's the same as XCF, then all it is is a image file that keeps the image exactly how you left it. Layers, resolution, even stuff like rulers and grids will be preserved, and it lets you pick up exactly where you left off.
My point is that when you convert it to PNG you won't get transparency, but it's extremely handy when making the sheet.