This achievement simply requires you to equip Effervescent/Rainbow quality gear in all slots except your Class Mod. That means you will need get at least 4 Effervescent/Rainbow quality guns, 1 shield, 1 grenade mod and 1 artifact. Effervescent/Rainbow quality items are exclusive to the Commander Lilith DLC and while some may drop for you on your first playthrough you may need to farm some afterwards to complete this achievement