I will second that the blue wire is probably the remote turn on, the yellow wire (10 gauge) is probably the factory amp power wire, and judging from the picture, the red wire is an 8 gauge likely for an aftermarket amp.
The best thing to do is get out a volt meter and see what voltage is on the wires. The power wires (yellow and red) should be +12VDC all the time and the remote turn-on (blue) should be +12VDC only when the radio is on.
It also appears that the RCA cords are running on the same side as the power wire, the "double" red wires on the right. It is best to run them on the opposite side to avoid interference in the signal.