Referencing custom fileds doesn't work

I tried referencing a custom field “color” in Kee->Form fields->Edit via {S:color}.
Unfortunately the reference is not replaced. I tried with enabling “KeePass placeholders” too but without success.
Any ideas? Is this a bug? A reference to {NOTES} works flawlessly.

Have you checked that you’re using the latest version of KeePass, Kee and KeePassRPC?

If so, please try with a new KeePass database and supply an example where it doesn’t work so we can investigate further (ideally include the kdbx file with just the problematic example and no master password)