If you are crediting the original artist (and even if appropriate providing a link to the original image either in the description or as the Source_Url of the upload), and as long as the original artist is ok with color edits (ex: they don’t have a DO NOT POST that does not permit color edits) then you should be ok.
The only problem with color edits is that changing the characters in the original image may run afoul of our Rule #1 - for example if you remove or change an OC in the original image, or change one of the characters into an OC, then we call that an ‘OC Edit’ and generally speaking those are Rule #1.
It looks like you ran into one artist once who didn’t want their work here, but other than that your uploads seem fine.
If you’re not sure though, and have something in mind that you’d like to do, feel free to PM me and I’ll ‘work the process’ to see if there’s any foreseeable problems with what you’re proposing. That’s no guarantee than an artist might not complain afterwards, which is their right, but at least then you’ll know that the image isn’t taken down due to something that was foreseeable.