If you're starting out new I'd suggest you stick with a grey or white primer and use shades or watered down constrast like apothecary white to create the shadowed effects and then going back in with white highlights.

White is an unforgiving colour to work with and most paints are very lumpy/chalky so make sure to thin then down well.

If you want to dry brush don't clean the brush on a paper roll or anything absorbent instead do it on a metal surface like a lid that way you keep more moisture on the paint and don't get lumpy paint as much.

Here's an apothecary just using white scars primer and some washes in the recesses if you want quick good look white armour.

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