Why flag color do not match still iOS - MacOS

We are fellow users and the Apple product teams do not participate in these user-supported communities. Therefore, "why" implementation questions will remain unanswered here because we simply don't have product team decision or omission information.

You can however, submit direct feedback to the Mail product team, though it is unlikely they will respond.

I cannot reproduce this. I don't use flags much, and I keep most of my mail stored under On My Mac, but for the sake of testing I took one message stored in one of the mailboxes for my iCloud account and flagged with the light blue color. In a few seconds it appeared with that same blue color in my iPhone as well.

What type of e-mail account (IMAP, Exchange), and which is the provider?

Flags in Apple Mail on 3 different Apple Computers marked as Green will appear as Green in my iPhone running iOS 16.3.1

If I mark the same e-mail on iOS on iPhone as Orange, it will appear as Orange in the 3 Apple Computers

The ability to change Colours of Flagged e-mail in iOS is contained in the link below

Flag emails in Mail on iPad - Apple Support (CA)