I used a whole bottle Evening Blue mixed with a whole box of Pearl Grey like DV said (which I had no trouble finding at my local Joann) in a 3/4 full bath tub and I'm very happy with mine.
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One thing to take note of with MOW's suit is the two separate pockets are a thicker material and take longer to dye, mine turned out a weird baby blue the first time and it took a couple more dyes and weathering to get them to match up. Also when you weather it go slowly and don't over do it. I went crazy the first time and had to remove all the color and re-dye the whole thing so subtlety and patience are your best friend.