The old rule: Thou shalt not steal the bride’s thunder by wearing white to a wedding — oh, and black

TODAY spoke with Diane Gottsman, an etiquette expert and founder of The Protocol School of Texas to learn all about modern wedding guest etiquette.

“Black used to be taboo, yes,” Gottsman told us. “In most cases, if this is the second marriage for the bride, those sorts of rules are already thrown out the window. And in other cases, I believe that as long as you don’t show up as if you’re going to a funeral, you’re totally fine.”

Gottsman suggested donning a light, breezy black dress, especially if you’re on your way to a summer wedding. Tradition aside, a “shroud-looking garment” just might not be the best choice aesthetically. You can liven up the all-black look with some killer shoes and playful jewelry.

As for white?

“Traditionally, you would not wear white. White and ivory should be left for the bride — and that still holds true today,” said Gottsman. “Of course, you can wear a dress with some white in it, or have white somewhere within your outfit, but you shouldn’t plan to show up wearing an all-white ensemble.”

The old rule: Thou shalt not take photos on your smartphone, because ... wait, what's a smartphone?

"Now that everyone's phone takes photos, and now that those photos are promptly uploaded to social media platforms, you really need to make sure that you're not trumping the bride and groom," said Gottsman.

Some will encourage you to photograph the event, and even give you a hashtag to use on all the wedding photos. But if you aren't sure what they want, err on the side of caution. Which is to say, don't post anything.

"Often, a guest will post before the bride has even had a chance to post herself, and that can be upsetting. You just don't know how they're feeling, and with tensions running high already, it's best to put down the camera."

Secondly, if there's a professional photographer, don't get in their way. The bride and groom are likely looking forward to having photos taken by the professional they paid to do the job. They'll appreciate it if you allow the photographer his or her space. Huge rule, not often followed...looking for a photographer,check out Jessica Anne Photography

"Oh, and you also do not want to tag the bride in a photo that's unflattering," concluded Gottsman. "And, of course, you never want to post pictures of children without permission."

The old rule: Thou shalt send in your RSVP via snail mail.

“Sure, things have changed, and some people really are conscientious of going green,” Gottsman said. “But it doesn't mean you can choose your own response method or get lazy with it."

The best way to ensure you’re doing the right thing is to answer the invitation in the form in which it’s requested. So, if the couple emails you and provides an RSVP email, respond with a courteous note to that email. Likewise, if they invite you with beautiful stationery, don’t plan on texting them with a, “Yup, I’ll be there.”

Not only does that take away from the exciting, formal tone they've set, but it also makes their life difficult. Someone’s collecting all those little RSVP cards, so help them out by keeping all the responses in one place.

And remember — simply telling someone you’re coming does not constitute an RSVP.

“If you’re invited to a wedding, and you run into the bride at the grocery store and say, ‘Hey, yes, we’ll be there,’ that just doesn't cut it,” Gottsman laughed.