From WoWWiki

Bonuses to Hit rating can only be obtained through Yellow gems and Orange gems.

Color	Name	Effect(s)
Yellow	[Rigid Bladestone]	+12 Hit Rating
	[Rigid Lionseye]	+10 Hit Rating
	[Rigid Dawnstone]	+8 Hit Rating
	[Rigid Golden Draenite]	+6 Hit Rating
	[Rigid Amber]	+4 Hit Rating
Orange	[Etched Fire Opal]	+4 Hit Rating	+5 Strength
	[Glinting Pyrestone]	+5 Hit Rating	+5 Agility
	[Glinting Fire Opal]	+4 Hit Rating	+5 Agility
	[Glinting Noble Topaz]	+4 Hit Rating	+4 Agility
	[Glinting Flame Spessarite]	+3 Hit Rating	+3 Agility
	[Nimble Fire Opal]	+4 Hit Rating	+5 Dodge Rating
	[Pristine Fire Opal]	+4 Hit Rating	+10 Attack Power