I’ve downloaded some wide skirts like this from the internet before, but I don’t remember from where. The problem is that the shoes show through the hem. I’ve tried all sorts of things in GIMP, editing the alpha files to be either black or white, etc., but nothing seems to work. It’s frustrating that these beautiful skirts go unused. Someone once posted instructions on Tumblr on how to fix this kind of issue, but I can’t find that post anywhere anymore. Could anyone advise on what to do?

Can you share the recolor + mesh? I have a few suspicions what the issue is, but it's easier to pinpoint the exact issue by looking at the files (likely material settings, possibly another thing).
It's most likely not something that can be fixed in Gimp, but it is likely fixable through SimPE.

Thanks, here are the mesh and rc.

Unless you plan to make a recolor with a shorter alpha for the skirt, the easiest fix is to change the "stdMatAlphaBlendMode" setting in the TXMTs for the Alpha 3+Alpha5 groups to "none" (+ "commit" and save). This should fix the see-through issue. Delete the cache files too (especially if the files don't seem to update - accessory+groups files).

If you want to edit the alpha, or use a transparent texture, I'd recommend a few other fixes on the mesh. The mesh parts have been layered a bit awkwardly, and the "blend" setting causes the shoes to jump to the front because the game can't distinguish which item is in the back and which is in the front.

This mini tutorial shows what's happening (but it's a bit more complicated to fix it for clothes - you'd have to put together the mesh and morphs differently, and swap over textures)
https://pforestsims.tumblr.com/post...-opacity-issues

Thank you so much for your help❤️ I will try these advices.