I hadn't realized there was a delay. Either I'm too used to waiting, or I don't login locally enough.

I use a solid background color because a lot of the time I login through a remote desktop connection. By default, remote desktop connections use the solid background color even if a background image is set, so that there's less information to send over the connection. With this in mind, I figured I would just stick with the solid color anyway, so that I saw the same thing locally and remotely.

According to the Microsoft Support page, this login delay bug does not affect remote desktop connections.