Hi Tim,
I am not sure if that's the only way or even the best way.
The best way to evaluate a cast is to open the image in photoshop and use the eye dropper tool to read the absolute RGB values in a neutral region, anything else is subjective. The RGB values on this image look correct as shown below
As I menioned I don't really see a cast on my NEC 4K pro display that has been calibrated with Xrite tool. I am not sure what kind of monitor or calibration tool you are using. If it's an iMac screen unfortunately it is not going to be that accurate even if you calibrate it, hence the best way is to check the RGB values.
I do feel the image can use some warming and add of contrast/saturation though
hope this helps