Apart from melee DPS all classes and specs have something going for them in each color.
Even when some specs ignore socket bonus for a certain superior gem attribute, there is still a mathematical decision - a choice - behind it.
For melee dps, however, there is no choice at all.
Enhancement Shaman might be an exception to this, but would they ever gem Mp5 (Infused)?
Spirit Casters:
Red = SP
Yellow = Crit, Hit, Haste, Int
Blue = Spirit
Mp5 Casters:
Red = SP
Yellow = Crit, Hit, Haste, Int
Blue = Mp5
Hunters:
Red = AP, Agi, ArP
Yellow = Crit, Hit, Haste, Int
Blue = Mp5, Stamina (Survival)
Tanks:
Red = Dodge, Parry, Expertise
Yellow = Defense, Hit, Haste, Crit
Blue = Stamina
Melee:
Red = Str, AP, Agi, Expertise, ArP
Yellow = Crit, Hit, Haste
Blue = >Nothing<
Suggestion: Expertise as a Blue gem attribute.
It's not always necessary, depending on gear, so it would be a choice.
Socket bonuses (with blue sockets) wouldn't be an illusion for Melee DPS anymore... we might actually use them.