On the "Recent unread topics"-page, accounts who are treated as guests display with a white name color.
However, in the actual thread, they are listed with an orange name color, similar (if not the same) as the old default user color.
If I may add a suggestion on top of that, I would suggest that perhaps it would be an idea to revert all instances of the guest user color to white since that no longer conflicts with the default user color. Not only would that free up the orange color for future use but I feel also that guests, since they are not actual users (anymore), it makes more sense to have colorless (i.e. white).
[attachment deleted by admin]