The blue followers are for the double stack 40 mags. I've never seen a blue follower for a 45XX series single stack mag.

The red/orange...ish followers were the first ones sent out with the 4506. Then came the yellow followers, used in all the 3rd Gen 45 mags.

The last were the black followers. The black followers also fitting all the previous mags and were the last iteration. I use the red and yellow followers in my range only mags, but for carry I only use the black followers. Regards 18DAI

__________________
7 +1 Rounds of hope & change