From WoWWiki

Bonuses for Critical strike rating can only be obtained through Yellow gems, Orange gems and Green gems.

Color	Name	Effect(s)
Meta	[Enigmatic Skyfire Diamond]	+12 Critical Strike Rating	5% Snare and Root Resist
Yellow	[Stone of Blades]	+12 Critical Strike Rating
	[Smooth Lionseye]	+10 Critical Strike Rating
	[Smooth Ornate Dawnstone]	+10 Critical Strike Rating
	[Smooth Dawnstone]	+8 Critical Strike Rating
	[Smooth Golden Draenite]	+6 Critical Strike Rating
	[Smooth Amber]	+4 Critical Strike Rating
Orange	[Assassin's Fire Opal]	+6 Critical Strike Rating	+5 Dodge Rating
	[Inscribed Pyrestone]	+5 Critical Strike Rating	+5 Strength
	[Enscribed Fire Opal]	+4 Critical Strike Rating	+5 Strength
	[Inscribed Noble Topaz]	+4 Critical Strike Rating	+4 Strength
	[Inscribed Flame Spessarite]	+3 Critical Strike Rating	+3 Strength
	[Inscribed Ornate Topaz]	+5 Critical Strike Rating	+10 Attack Power
	[Wicked Pyrestone]	+5 Critical Strike Rating	+10 Attack Power
	[Deadly Fire Opal]	+5 Critical Strike Rating	+8 Attack Power
	[Wicked Noble Topaz]	+4 Critical Strike Rating	+8 Attack Power
	[Unstable Citrine]	+4 Critical Strike Rating	+8 Attack Power
	[Wicked Flame Spessarite]	+3 Critical Strike Rating	+6 Attack Power
Green	[Jagged Seaspray Emerald]	+5 Critical Strike Rating	+7 Stamina
	[Jagged Chrysoprase]	+5 Critical Strike Rating	+6 Stamina
	[Jagged Talasite]	+4 Critical Strike Rating	+6 Stamina
	[Barbed Deep Peridot]	+4 Critical Strike Rating	+3 Stamina
	[Jagged Deep Peridot]	+3 Critical Strike Rating	+4 Stamina
	[Sundered Chrysoprase]	+5 Critical Strike Rating	2 mana every 5 sec