Custom white balance for studio flash.

[vinniemac]

New Sony user here, trying to get my head around all of the differences from Fuji 😬 

I’ve figured out most of the settings, but can’t find any answers on how to do a custom white balance for studio flash. The custom setting option only seems to be based on measuring ambient light. The only workaround I can think of is to set an approximate kelvin value and then shoot a grey card and fix it in post, but I’d much prefer to get it right in camera. 
 

camera is an A7CR

TIA

Vinnie