As an Erudite Magician with superior intelligence I know a trick to remember temp bags. It's possible to color color specific bags.
Open the bag you want to color.
Right click the background of that bag window.
Click Background > Texture
Click Background > Tint Color
Select a color or set a custom one and click accept.
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I find setting the Temp bag slots to a bright orange helps me remember the no rent.
(this works on any ui window that has those options)