Inky (the cyan ghost)
Clyde (the orange ghost)
Pinky (the pink ghost)
Blinky (the red ghost)
 
Correct Answer: Inky (the cyan ghost)

A brief explanation why…

In the original Pac Man (released in October 1980 as an arcade game in Japan), the red ghost Blinky was written to follow behind Pac-Man, Pinky is tasked with getting in front of Pac-Man, Clyde would sometimes behave as Blinky and other times wander off on his own, while Inky the blue ghost was intended to be unpredictable: he might behave as Blinky, Pinky or Clyde.

The ghosts were described in Japanese as having the following character personalities:

Blinky: "Oikake" or "Chaser"

Pinky: "Machibuse" or "Ambusher"

Inky: "Kimagure" or "Fickle"

Clyde: "Otoboke" or "Feigned Ignorance"