For hue he noticed the correct trend but misattributed the reason. The reason for the color shift in sunlit shadows is that outdoors the fill light is blue-tone

For hue he noticed the correct trend but misattributed the reason. The reason for the color shift in sunlit shadows is that outdoors the fill light is blue-toned due to Raleigh scattering while the direct light is from the sun and is closer to yellow.