My Google Pixel 9 Pro just got an update to Material Expressive, and it makes the dynamic colors in #Conversations_im way too intense for my taste.
Remember that you can turn off 'Colorful chat bubbles' in the interface settings.

I don't know - at this point, the 'primary and secondary surface' theme colors maybe aren't meant for things like chat bubbles anymore. Anyway, the setting to turn them off is already there. Or go back to the default (non-dynamic) theme.