"WE DIDN'T want to make a fashiony interior," says the Paris-based designer Michael Coorengel. "For us, decoration should look almost natural." So, when he and his partner, Jean-Pierre Calvagrac, set out to rejuvenate an 18th-century manor house in the Bordeaux wine region, it made sense to them to re-create a Louis XVI–style decor. Period appropriate, yes, but upon first sight, the color palette seems strikingly, almost shockingly, modern. Walls are bright green, sunny yellow, vivid turquoise, and deep teal. Yet, Coorengel points out, these are exactly the type of shades that originally would have been used at Versailles. After all, colors fade over 300 years. "Back then, Versailles was psychedelic, multicolored, like being in space," he says. "It was the standard for design. Imagine having a palace done by Zaha…