Confused about D50, D65, and CCT in white balance and color calibration modules

Well, no. 6500K is daylight under an overcast sky (or open shade). Direct sunlight at noon is closer to 5000K. The exact value will probably vary a bit due to light scattering (blue is scattered more than red).
And according to NASA “raw” sunlight, before it hits the earth’s atmosphere, is 5772 K (of course independent of time of day).

Also, that 6500K in the white balance module is a reference value, unrelated to the actual image. It serves to provide a fixed starting point for the color calibration module.

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