what beautiful photos !!! i suspected before viewing that your Pieris might be variagated ( white stripes in foliage )...your pictures confirm this and point to the shoot being what is called " reversion " back to plain green leaves. These leaves are always more vigourous due to more chlorophyl and if not removed can take over the shrub spoiling the variagated effect you paid for in the first place .
once again nice pics and btw my very first post on this or any garden group !