If you have a lot of types of items in one chest, it can be confusing. I feel like if you made different slots in a chest be colored by their creative inventory category, that would help.

This makes sense. I'm not sure if it will be possible for the modded storages but for standard chests sure.
Always using the same colour for given category might be a problem for modded also.

Thanks for the suggestion!

Right. Another implementation might be adding whitespace in between different creative categories

as in:

item, item, item, empty slot, item, item

Yes, just an empty slot(s).

with the changes in 1.18.2 I expect major changes in Items organisation and handling. So I prefer to wait for 1.19 before implementing something like this

Sounds good. Can't wait to see what's next.