If the light is right, a deer will be able to see you inside. For instance, if the sun is shining into your blind from behind the deer, they can see in. BUT if the deer is looking toward the sun and the sun is behind you and the blind, it will look black inside, and they won't be able to see you!
It's a good idea to wear black, or at least dark clothing while hunting from inside a blind, that will help in keeping you hidden! Also, keep your movements slow jsut in case!