I'd suggest to judge correct polarity by ear. Do a simple listening test: 1) connect your speakers up to your amp. Play a track with vocals. 2) Then ON ONE SPEAKER only, switch the positive and negative wires and listen again. The wire orientation that sounds the most focused, voice in between your two speakers, is the correct polarity, regardless of what colors or what you think is +, -.
Speaker terminal polarity
I just unpacked my Cary 300B-SE mono blocks after being in storage for over 15 years. Both speaker outputs (on each amp) look identical (not color coded) and neither is labeled + or -. I tried a continuity test against the amp chassis and both terminals read the same. How do I determine + from -? Does it matter as long as I have each amp wired to its corresponding speaker the same way?
I must have asked this question when I got the amps 17 years ago, but can't locate the thread. Standing by with red and black sharpie pens if necessary.