Something to do with the moon up, tried a narrowband image using Hb instead of S2 not sure about the colour but at least the stars are white.
Taken with 18" f4.5 Newt. Qhy9
Ha 4x600sec O3 6x600 sec Hb 11x900sec.
Had to crop some off as the camera and filter wheel unscrewed a little sometime during the exposures
you have to love screw adaptors.
Clear skies Ken.
sorry small jpeg only.