1968 Plymouth:
AA1 = "buffed silver metallic" an extra cost color (A=silver roof, A=silver body, 1=monotone paint style)
S6R = Sport vinyl bucket seat interior "RED"
U = UDF = Upper Door Frame paint color - R = "burgundy metallic"
B = Buffed paint = sales code 708
S = Stripes = sales code 311 = "BLACK" sport stripes

in 1968 the S6R interior was simply "RED" for Plymouth