WoWDB

The blue Hatchling Skyscreamer can be found in the same area where you go for the daily Preventing a Future Threat (A) / Preventing a Future Threat (H). When those baby pterodactyls are feared off for the daily quests, they can re-spawn as a blue version.

You will need to be on the daily to be able to obtain this achievement.

To add to NPC_scan, use command line: /npcscan add 70215 Hatchling Skyscreamer

It will only alert you to the presence of a blue hatchling, unfortunately, because it doesn't have its own unique name to go along with its npc id. You will just have to keep a careful lookout for it. More than one person can get credit for this if timed and positioned correctly.

And when you get it... Congrats! You finally got a blue response. =P

Edit: I've heard reports that you don't need to be on the daily to scare the little guys, so I've crossed out the bold part.