Convert the image of the grey card you captured in the camera to JPG. Download the file to a computer or smart device and read the value from the EIF.
However, different sensors do not have identical responses to light and color. The color temp that is ideal for the R6 is probably NOT the ideal color temp for your drone.
If the drone allows you to manually set a color temp, then doesn’t also allow you to capture a test image to use as a WB setpoint?
I forgot to add that WB is more than setting a color temperature. There is also the matter of color tint, which is what varies the most from one sensor to the next.
Also, I find that a daylight color temperature of 5200 often works well for capturing the lighting as I remembered it, especially if the lighting is varying as I shoot. If the drone can save raw images, then the white balance can be set later on a computer. Else, one might try setting the white balance on the drone to "daylight" or to 5200.
12/05/2023: New firmware updates are available.
09/26/2023: New firmware updates are available.
08/18/2023: Canon EOS R5 C training series is released.
07/31/2023: New firmware updates are available.
05/18/2023: New firmware updates are available.
03/30/2023: New firmware updates are available.