Hi Kathy,

it is a while since I worked with that, so I can only guess based on the code of the theme (https://github.com/florianbrinkmann/photographus/blob/9dc7296cb720a230f2fe1e8a19e7fe16f5503ea5/inc/front-page-panel-functions.php#L346). It seems that the callback function gets an object as the first parameter that includes the panel number. And with that, I can use get_theme_mod() to get the new value (Weston writes in his comment to the announcement post that you will get the new value there in the Customizer context).

Hope that helps!

Best,
Florian