One of my favorite 45s out of Philadelphia is "Color Blind" by Frankie Beverly's Raw Soul. From start to finish it knocks me out; it's fantastic both musically and lyrically.
The tune starts off a with a 1-2 punch courtesy of some horns, and then just kicks into a dense groove that carries the song. There's a tambourine and a conga going throughtout that sandwiches the percussion nicely. Lyrically, it's reflective as well as intense. And the vocal harmony breakdown in the middle....great.
The lyrics are still right on the money. As Frankie sings, "What color is harmony?".
Check out a snippet here.