From WoWWiki

Bonuses for Healing can only be obtained through Red gems, Orange gems and Purple gems, as well as a single Meta gem.

Color	Name	Effect(s)
Red	[Teardrop Tourmaline]	+9 Healing
	[Teardrop Blood Garnet]	+13 Healing
	[Teardrop Living Ruby]	+18 Healing
	[Teardrop Crimson Spinel]	+22 Healing
	[Kailee's Rose]	+26 Healing
Orange	[Luminous Flame Spessarite]	+7 Healing	+3 Intellect
	[Luminous Noble Topaz]	+9 Healing	+4 Intellect
	[Luminous Fire Opal]	+11 Healing	+4 Intellect
	[Luminous Pyrestone]	+11 Healing	+5 Intellect
	[Iridescent Fire Opal]	+11 Healing	+4 Spell Critical
	[Durable Fire Opal]	+11 Healing	+4 Resilience
Purple	[Royal Shadow Draenite]	+7 Healing	+1 Mana every 5 sec
	[Royal Nightseye]	+9 Healing	+2 Mana every 5 sec
	[Royal Tanzanite]	+11 Healing	+2 Mana every 5 sec
	[Royal Shadowsong Amethyst]	+11 Healing	+2 Mana every 5 sec
	[Purified Jaggal Pearl]	+7 Healing	+3 Spirit
	[Unstable Sapphire]	+9 Healing	+4 Spirit
	[Purified Shadow Pearl]	+9 Healing	+4 Spirit
	[Imperial Tanzanite]	+9 Healing	+5 Spirit
	[Purified Shadowsong Amethyst]	+11 Healing	+5 Spirit
	[Blessed Tanzanite]	+11 Healing	+6 Stamina
	[Soothing Amethyst]	+11 Healing	+6 Stamina
Meta	[Bracing Earthstorm Diamond]	+26 Healing	2% Reduced Threat