For me the Black and Blue Super Platinum are the best shaving of the the Gillette 7 O'clock blades. I prefer them in this order Czech made Blue Super Platinum, Russian made Blue Super Platinum, Indian made Black Super Platinum, and Russian made Yellow SharpEdge. The two Greens have never worked well with my face but many here love them.
As for the differences between the blades, the Black and Blue are Platinum coated. The Yellow are also coated but I'm not sure what material they're coated with. Telfon pehaps? If someone knows for sure please correct me as I am not positive. I read here a long time ago that the Greens are uncoated but again I am not positive. The blades are also made in different countries.
Sadly, the Blues have all but disappeared from the market place over the last year. You can find them in single packs here and there but it's been a while since I seen them for sale in large quantities. I hope they make a comeback like the regular Gillette Platinums have done recently.
The Czech made blues are one of my faves. Right up there with Personna Meds & Labs. But not cheap and kinda hard to find. Which is why I don't bother and go with the easy to source Personnas. The Blacks are harsh are me.
Gillette 7 O'Clock Blacks are by far my all time favorite DE blade. I have never tried anything that feels as sharp and smooth for me. The blues are second in my opinion.
I've used the blues, blacks, and yellows. The blues might be the best blade I've ever used (which is unfortunate, since they're no longer available). The yellows are a tad less smooth, but still a great blade. I found the blacks to be a bit harsh, but at that point I had already settled on the blues for a 100-blade purchase.