This is a very simple, beginner tip but something that's easy to miss. We've spoken about VIP Mailbox and alerts before but one thing that we missed was a little troubleshooting. One user over at Support forums asked why some contacts are bold and some are grayed out when trying to add VIP contacts.
When you try to add VIP contacts, you might find that not all contacts can be added. The grayed out ones cannot be added to the VIP list. Here's why this happens.
VIP Contacts is specifically related to the Mail app. It's not functional elsewhere. The VIP contact feature (introduced in iOS 6) is Apple's feature to enable easier mail sorting. With VIP mailbox, you can read the most important mails first and then go over to your inbox to read other emails. It's basically prioritization.
I won't go over how to add a contact to the VIP list. We've covered that already and the steps remain the same for iOS 7.
However, when you are picking a contact, you find that some are grayed out (and can't be added) while some are darkened/bold (and can be added). The answer is simple:
The answer is simple: the contacts without email addresses cannot be added to the VIP list for Mail. Those with email addresses can be.
Since the VIP feature is specifically for Mail, it's obvious that the list contains email addresses. If a contact does not have an email address listed, there is no point in adding the contact to the VIP list and so Apple grays these contacts out. Makes them “disabled” so to speak.
The rest of the contacts that you see, bold ones, can be added to the list because these have email addresses.
So that's about it. If you make sure that a contact has an email address, you'll be able to add the contact to the VIP list.