AFAIK there are no good reasonably priced in wall speakers. You could try some Bohlander-Graebner in walls. However, they are not inexpensive and need some grill material in front. Hyfi's suggestion of hanging a painting in front is a good one. The fabric should be as acoustically transparent as possible.
BTW, theaters usually have the main speakers behind the screen which is made of acoustically transparent material.

It seems that you are more concerned with aesthetics than audio quality. Most posters here are more concerned with sound than looks.

Welcome to AR!