Seems to me you're confusing brightness with color temperature, Heather. You've gotten plenty of good advice above about color materials, their resistance to manipulation compared to b&w. Metering off a gray card never hurt anyone, and assessing the brightness range of the situation with your spot meter realative to the brightness range of your film is a must. (Working with several color transparency films, I've found they do vary on this point). But if your question is really about how to apply zone system thinking to the situation, it seems to me the answer is that, for the purposes of exposure, you want to see it in b&w, paying attention only to brightness. You can certainly take advantage of the vital zone system concepts of "place" and "fall" to manipulate the exposure to look the way you'd like. That said, of course color provides depth where contrast does in b&w. So images that would look flat in b&w may work because of color--but this is not really a matter of exposure. Some photographers go nuts reading color temperature in b&w, since film "sees" certain colors more intensely than others. They're effectively asking the same question you are in b&w. Many photographers survive without worrying about this, in b&w and color. Best of luck,
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