The goal of any portrait is to draw the eye to the faces. Bold patterns and bright colors will only distract from the portrait. Dark earth tones of brown, burgundy, green or blue work well with a medium dark background. Black and shades of gray also look good against a dark or even black background.
High Key portraits (read, white background) look good with khakis and white shirts. Or, pastel blues, creams, greens. The goal is to create contrast between the faces and the background. We want the faces to dominate the portrait and not the wardrobe.
There are exceptions to every rule. If your overall brand identity is tied to a particular color, then let's go with that.
Avoid trendy jewelry
Avoid frosted eye shadow or lipstick
Long sleeves look best
Make sure all outfits are freshly pressed
Men should be clean shaven or facial hair carefully trimmed
Men have hair cut several days before the photography session
Women know best about their hair