Years ago I saw paper go by, a NATO long-term "sky survey" - a color-calibrated camera watching the full hemisphere of the daytime sky somewhere in Spain(?) for

Years ago I saw paper go by, a NATO long-term "sky survey" - a color-calibrated camera watching the full hemisphere of the daytime sky somewhere in Spain(?) for year or so. As I recall it, the chromaticity of the Sun, when more than a couple of tens of degrees above the horizon, regardless of cloud cover, was nothing but white.