The best type would be an exploded tip nylon brush for use with water or solvent based wood paints.
Yes, 896 colorant is compatible with Hemp Shield. Only care should be taken that deep base (solid color tints) many have slower dry times than normal.
Mill Glaze is a common problem with mill cut wood which is manufactured using a dull planning blade. The surface of the wood becomes heated bringing the wood tannins and acids up to the surface, heating and, than sealing the wood. The wood will then not accept stains. There are two basic ways to deal with mill glaze. The first is exposure to weather which will open the wood naturally over time. The wood may than be stained. The second method is using
a commercially available Wood Glaze Remover. These materials are a combination of water, solvent and wetting agents which dissolve the glaze and open the wood for staining. If you do not remove the glaze and attempt to wood floor stains, the wood will stain unevenly and you will have blotches in the look of the deck.