The Whitelist/Blacklist tab allows you to change your blacklist/whitelist settings for the Profile that is showing at the top of the page, as seen above. To make sure that you are adding changes to the correct Profile, please ensure you are only making changes to this area when you have the correct pairing above. Use the drop down box to change the current OU that you are viewing/editing, then you can make changes to the profile attached to this OU.
For example, when I select the Support Troubleshooting OU it looks like this in the dashboard:
We can see that the profile attached to this OU is the "Support Test", so we know that any changes we make to the Blacklist/Whitelist or to the YouTube filter will apply to the "Support Test" profile which we have attached to the Support Troubleshooting OU. You can change which profile is attached to which OU in the Account Settings > Organizational Units section. See Creating a Settings Profile for more information.