You don't have the yellow/gold border because you couldn't actually purchase the Hive Disruptor perk to fill all the bubbles. Technically, the perk is still there; it's just hidden. I noticed this on one of the after mission reports and saw that it was still assigning xp to that perk, even after it was disabled. It really doesn't affect the weapon much, to be honest. Hive Disruptor causes pretty low damage that I've seen thus far.