PC Jacket for upcoming event

[CMcG]

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So my main concern is, Would using the matching fabric for the lapels just tone the jacket down, or turn it off?

I'm no tailor but I'll venture an uneducated opinion. It would certainly tone the jacket down to use all one fabric and, though I'm not sure that it would actually ruin it, it would look better with the fancy lapels. You might scrimp a bit and use the matching fabric on the facing. You might also try to get your hands on some corded or grosgrain silk, if peau de soie is too hard to come by. I think the idea is that all of those are very smooth, lustrous materials with a slightly dull finish, rather than really shiny satin. Maybe even look for a cheaper synthetic alternative with the same effect?