The most common contemporary formal look seems to use either a more limited colour palette or, as Chrisupyonder suggested, monochromatic. Sometimes a clan tartan kilt is worn, sometimes low contrast fashion tartans (think grey on black), or sometimes even solid colours. Pared down versions of traditional jackets are offered without fancy cuffs, or with buttons that might be black or antiqued metal. Shirts can be white but are sometimes black, and large wing collars are often found.

The ruche knot (scrunchy knot) on an ascot tie is often seen. Strangely enough, I've also often seen these sorts of outfits worn with ghillie brogues, which seems to go against the general simplification of the look. I don't mind the look, but I'd go with plain, well shined oxfords and a stock tie instead. I'd also think a more modern sporran might work nicely with them, like one with a blacked cantle to go with the buttons.

Here's some pics: