I use Fender strings a lot of the time , so here goes:
Black silk ends: 7150 nickel-plated hex core. They usually use these or a version without the black silk for most bridge through basses they sell.
Red silk ends: 7350 Stainless steel
Yellow silk ends: 7150 original nickels
Powder blue silk: 8250 roundcore nickels taperwounds, used on the body through basses they sell.
These are the roundwound models they sell. I hope that will help you. As with most companies, they usually come with medium gauge sets on the basses when sold.