Apple Mail inbox contact photos/icons/avatars are always greyscale, not colour?

Hi,

I'm running Sequoia 15.4.1. In Apple Mail, I want to have colour contact photos/icons/avatars or whatever you want to call them, the small circular thing next to each email in your inbox. Mine are always greyscale and plain, just a letter in them, but I keep seeing photos of Apple mail, where they are all coloured, and I would like to get mine to look like this. I can't see anything in the settings, so how is it done, please? Not just for regular contacts, but for all emails. I have tried dark/light mode and they are both greyscale for the icons.

Could anyone help me out please? Thanks.