How to Display Covers on Kindle Color for Books Not Bought on Amazon (Using Calibre)

Hello,

I recently got a Kindle Color and I'm using Calibre to transfer my ebooks — including books not purchased from Amazon.
However, the covers don't show up properly on the Kindle home screen.

I’ve installed the necessary plugins (KFX Input/Output), and tried converting to KFX and MOBI, but the issue remains.

➡️ What is the best format to use to ensure cover compatibility on the Kindle Color?
➡️ Are there any specific steps I should follow (metadata editing, file renaming, sideloading method)?
➡️ Does cover display work differently with the new Kindle Color models?

Thanks a lot for your help!
lilik