Iris, and color issues

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if the iris is open, will this make the colors seem washed out a bit?, i read this in a book, and have wondered why some of my shots dont have the best color to them, even though i whitebalance all the time, and have my scene files set to default most of the time. The book said that 4.5 is an optimal aperature size for best skintone colors. Can anyone tell me if this is correct?