I use spot metering and shoot manual 99.9% of the time, and if there's either a white jersery or pants I meter off that and dial in my settings so EC is at least +2/3. I then shoot a couple of test shots and check the histogram. Unless it's a sunny day and cap shadows are present, I try not to blow out the whites.
You can meter off anything really. The key is knowing that a dead middle EC reading represents the mid-tone for whatever color you're metering. For instance, if you shoot white snow with a middle EC reading it's gonna come out kinda gray. But if you give it a couple bumps of +EC, it will be white. Dark blue shot at middle EC will produce the mid-tone of that color. With a couple of clicks of -EC, the dark blue will be dark blue.
MkII x 2 | Rebel XT | EF-S 18-55mm 3.5-5.6 | 17-40mm 4 L | 50mm 1.8 | 85mm 1.8 | 70-200mm 2.8L | 300 2.8L IS | 1.4x & 2x TCs | Lowepro Slingshot 300 AW | 580ex II
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