If Safari's menu bar isn't updating to match Momentum's photo color, changing your Safari Tab layout to Compact mode should provide a fix.
Updating your Safari Tab Preferences
- Press ⌘ Command + , to open Safari's preferences.
- Select the Tabs section, and choose the Compact Tab layout.
- Select the Advanced section and make sure Show color in Compact Tab Bar is checked.
Now, you should see the color of Safari's menu bar change to match your Momentum Photo! You can also have it match a Custom color in the Theme section of the General Settings.