I began to think that either I was cursed, or the stones were bugged. I have been on a collection spree the past couple of days and probably captured at least 30 new pets. I finally got one while capturing a beetle in Uldum. They don't seem to "drop" very often. The one I got was the blue ...

I summoned mine repeatedly to see if it would change colors, but alas it did not. This is unfortunate because this particular pet had always been a color-changing one, ever since vanilla. Seems like now it only displays the darker color.