Hi Kristin!

So, I take it you have your firstnamelastname.com AND firstnamemiddlename.com

You can really go either way. However, whichever way you go, it needs to be on all of your branding.

For legal stuff, contracts and etc - you will need to include your last name. So even if you use Kristina Blair everywhere, for legal stuff, you can add your last name so that it's Kristina Blair Colpitts.

Hope that helps! Let me know,
Nicole