The tree swallow is commonly mistaken to be a bluebird, simply because of its coloring. However, the tree swallow does not have an orange breast, instead it's simply a dark blue on top, with a white breast.
Tree swallows will often take refuge in the houses of the bluebirds, which is not really a bad thing. Tree swallows have almost no threat to the bluebirds other than taking their living areas.

Below are pictures of tree swallow eggs.