As far as I am aware there are no front door decor police :)
Seriously, terra cotta pots are universally accepted- make up some nice ones and if you don't like the way they look relocate them.

Is there a third color you are using for flowering plants? Yellow or pink or purple or blue would be very nice with your color scheme!
Maybe some dusty miller gray and dark as black pansies, black glass rock accents or glass pebbles as mulch- play with it.

I think mixing glazed black pots and your terra cotta ones will look great!!!