What did the flag look like?

Answer 1

There was no official Confederate flag. At Fort Sumter, when the Confederates captured it, they raised an odd looking flag that represented the 7 rebellious states. Later the so-called flag came to be individual battle flags for certain Confederate armies. To use a "modern idea" of the Southern flag, it best can be describes as gray-blue and red with crossed bars containing stars to represent states in the Confederacy. In modern times the so-called Confederate flag is denoted as the old fashioned "stars and bars" flag that for a piece of time represented the 4 year confederacy.

As an aside, Washington DC had slavery until 1862. Those slaves lived under an American flag. The border states during the war also had slaves living under the Ole' red white & blue.