You can also disable f.lux for specific apps, just click on the menu icon when the app is open, and you'll find the option under Disable > for Photoshop.
I used to do that for a few programs but it was always so jarring seeing the transition happen back and forth when I would tab out of Photoshop to the Finder or another app. Now I just disable for an hour if I'm doing color sensitive work at night.
I end up just lowering the strength when I'm using certain apps - I wish that was an option rather than completely disabling.
Disable for 1hour works great most of the time.
Going straight from full-blown f.lux to "disabled", everything looks extremely blue and harsh to me, and still doesn't look natural, so I prefer a lighter touch of evening mode.