the all black theme and all white theme are more difficult to read after using a competitor platform for many years I can definitely say that the color themes you have are hard on the eyes. With everything being the same color it all just jumbled together and is hard to differentiate. Black left menu with white conversation on the right is pretty helpful.
And even better is the ability to customize colors to be more personal for the users. To me this is all important because a user has communications screens up all day everyday and ease on the eyes and an aesthetically pleasing interface is very important.