Guests coordinate with wedding colors

If you were going to request all guests wear one specific color, I would probably choose black. Just because most people already have these items in their wardrobe, in case they do not want to purchase something new for the wedding. Plus, black is the easiest of these colors to find year round in stores. And black is always elegant.

Honestly, it's not a great plan to dictate what your guests wear, even if it's just a color. They really don't need to coordinate with your colors. Plus, as common as black can be for wedding attire, almost all of my friends have 2-3 dresses they recycle for weddings and they're all lighter colors (many still operate under the assumption that you shouldn't wear black to a wedding) and your guests could be the same. You can state semi formal, but leave out any color requirements.

You shouldn’t dictate what colors your guests can wear.

I know a lot of my FH's family and my family asked about what our colors were so they can coordinate. I know at my FH's cousin wedding pretty much everyone color coordinated also her c olors were blue and silver and everyone wore either blue or silver.

We haven't asked anyone to wear a certain color but we feel most people will end up wearing purple as that is one of our main colors.