Ortofon 2M Bronze

I gave you a link, it has nothing to do with the magnets, it's about cartridge inductance and the difference is so little that you will hardly notice. The difference is cartridge inductance (700mH for Blue and 630mH for Bronze), 1db higher channel separation for Bronze and 0.5mV higher output for Blue. The ortofon only recommend to use them like that, but it's not mandatory and there are people who use Blue on Black for example. 

There are differences and Ortofon chose a different motor so they have their reasons. May be silver wire vs. copper, who knows? But it was important enough that I'd go with Ortofon's recommendation.

That’s close to right...

red: copper generator / elliptical bonded
silver: silver generator / elliptical bonded
blue: copper generator / elliptical nude
bronce: silver generator / fine line nude
black: silver generator / shibata nude

”silver generator” means silver-coated copper wire.

Thats all!

Soundwise we made some comparisons and found out
that the diamond tip makes a difference... the generator
close to nothing.

There might be a selectional process at Ortofon but in
some cases the cheaper cartridge outperformed more
expensive ones.

Price/performance wise the silver is maybe the worst.