Spell Level: 12 (11)
Spell Name: Convoke Shadow
Class: War
Appearance: Skeleton
Hit Points: 200
Swing Damage: 16
Bash Damage: 6
Kick Damage: N/A
Backstab: N/A
Lifetap Damage: N/A
Skills: Bash
Source corroborates with wiki. the (11) is the highest level the pet can be. Should def not be able to summon a light blue pet at lvl 12.
http://www.necrotalk.com/showthread.php?t=2840
Also, the last time you are able to summon a yellow pet is level 8.