There are certain colors that naturally photography really, really well. Red is one of those colors.
Aside from my technical reasoning in support of People Wearing Red (is there a support group?), here are a few more good ones...
Red is the color of Christmas, Valentine's Day and the Fourth of July. So let's imagine… You and your family come in wearing the outfits pictured below. I take your pictures. You hang the beautiful, oversized portrait that results right above your mantel. When you look at that picture, to your relief, it won't look dated or "too seasonal". You are wearing red but not in a "we're celebrating a holiday" type of way. (And notice, you are not all match-matchy about wearing red. That is also good.)
Anyone can wear red - child, adult, male, female. Heck, you could even dress your dog in red if you wanted. The same may not go for pink or turquoise. Fido is just not that into pink.
Red goes nicely with any neutral color - white, black, khaki, grey, brown. Oh, and denim. Red and denim are awesome together.
Red is not boring.
Red sticks out. If we have a neutral background, wearing red will make you POP! out. (In a good way, I promise!)
My last reason for wearing red? Red and white were my high school colors. Go Niles West! (Sorry, I couldn't resist.)