True White (Mixing) is a formula meant for mixing into other colors easily and smoothly to lighten them and create tints. In the WynnColor System, we use this exclusively in our form shadows to pull them forward and set them in front of the rest of the tattoo.
Raw White (Opaque/Packing) is thicker due to a higher pigment load. It is best for highlights, but can also be mixed into other colors.
Raw White can be used like a mixing White without causing any real issues, just be a bit different/thicker to work with. it can actually give slightly brighter results some artists enjoy using more, or even go in easier at the risk of being overpowering.
But true White really doesn’t do well on its own for packing, so I keep that in mind.