Fix unclear text in broadcast message view.

### What does this MR do?
Fix weird text instructions on the broadcast message page.

### Why was this MR needed?
The existing text was extremely confusing. It read: Hex values as 3 double digit numbers, starting with a # sign. Hex colors are not always "digits" and saying "3 double digit numbers" is extremely confusing. Just change this to say 6 character hex values starting with a # sign.