Q. I am editing a manuscript that uses quotations from British texts. Can I silently change British spellings (such as “colour”) into American spellings in quotations?
A. Although it’s common to do this in the main text of a manuscript that has crossed the pond, I wouldn’t do it within quotations, partly out of respect for the original and partly because if I failed to catch every last Britishism, I would render the quotation inconsistent and violate my primary rule of copyediting: First, do no harm. If you decide to change the spellings, you could note somewhere that quotations have been edited for spelling and punctuation. For a list of permissible changes to quotations, please see CMOS 13.7.