No color shows up well if it is under a pile of leaves.
In heavy leaves (or deep snow) bright colors are not enough to insure you will find your disc. Understanding how discs finish their flights is the key to finding them. Shots which hyzer at the end will skip up and stay on top. Shots which anhyzer will bury into the stuff. Nose up skips up, nose down buries. So don't worry if you are throwing a hyzer. Send out a spotter if you are throwing an anhyzer.
In casual rounds we often ignore honors to determine driving order. We have someone throwing a hyzer line throw then go spot.
I agree, no color shows well from under the leaves. I remember spending 45 minutes of kicking leaf piles around to help a friend find his day glow yellow disc that buried under brown leaves. It ended up being right where we started, found it during the second pass.
If I had to pick a color, I'd go with bright pink, it seems to stand out in any season. But, I think Mark and Jeff are right, spotters are the key if you're throwing toward a mass of leaves.