When Butch Hartman unveiled Sparky at the Comic Con, he was colored blue.
His character is modeled after Rick Moranis' Louis Tully character in "Ghostbusters" - a hangdog, hard-luck type who means well but is kind of a doofus.
He and Cosmo are the only main characters to never wear Timmy's hat (Timmy wear the hat almost every episode, Poof in Sooper Poof (since he was adopted by Timmy's parents) and Beach Blanket Bozos, and Wanda in (Tons of Timmys).
Instead of world-changing magic in line with the chaotic wishmastering of Cosmo and Wanda (and sometimes Poof), Sparky possesses "dog magic," allowing him to conjure up bones, fire hydrants, and the like. His "wand" is the star on his tail.
One of Sparky's early sketches looks similar to Vicky's dog, Doidle.
Before the first air of "Fairly OddPet", it was speculated that the dog could have died during the events of the live-action movies (since Earth dogs live around 15 years, and Sparky seemed older than a puppy on the artwork revealed during Comic-Con). However, in "Fairly OddPet" Sparky states that "fairy dogs can't die", making this theory unacceptable.