Apparently the black armor is sold out already, at least for European PaB customers. I do not know if this also applies for US PaB.
The black ones are apparently discontinued being leftovers from the 7015 Viking Warrior vs. Fenris Wolf and 2006 KKII rogue knights production while the silver ones are still in production and part of the newer Fantasy Era castle line. I expect that this silver armor will therefore remain available for a longer period of time. At least, let's hope it will be.
I think Lego parted out some special pieces from the 5615 The Knight impulse set which explains the availability of the torso's and armor pieces. Unfortunately, they forgot to include the silver helmet and the crown shield.
Upper part no.1266 seems to be the torso used on the 5614 Good Wizard impulse set by the way except for the different color hands.