I shoot RAW, and I use a grey card. I'm learning to use my X-rite passport too.


I use remote flash a decent amount. In order to know what gels to put on the flash to match ambient light, I shoot the grey card, review with an RGB histogram, and adjust K and WB SHIFT to get accurate color in-camera. This also helps me pick the correct gel(s) to put on the flashes to match ambient. That's something you can't fix by changing the white balance values during RAW conversion.