The letter "A" (for "army") is formed by seven steps indicating the numerical designation of the unit. The colors suggest the three basic combat branches which make up a field army - blue for infantry, red for artillery, and yellow for armor (cavalry).
Veterans of the Seventh Army wore a tab reading "Seven Steps to Hell" under the patch, but this tab was never officially authorized.
On second picture shown old patch that was sold in 2015 for 115$.