My take on it would be:
Bright color = good
Sexy or revealing = bad
Feels "dressed up" = good
Feels like what you'd actually wear to the office = bad
Sparkly, feathers, sequins, etc. = good
Feels like what you'd actually wear to Mardi Gras = very, very bad.
My interpretation of "Mardi Gras-themed business formal" would be either a black dress or long skirt, with a gold, green, or purple shirt/jacket, and more accessories (belt, jewelry, handbag) than I would usually wear. And at least one of these items should be sparkly or shiny. My thighs/chest/stomach would be covered - and not just by a little piece of see-through or skin-tight fabric - and I'd wear black high heels, because everything looks dressier with black high heels, even though I'd probably break an ankle :-)