[Carl]

Would a A) grey card or B) White card imaged at noon give more accurate star colours when set as the CWB for astro imaging with a modified DSLR camera? And C) would this have an adverse effect when trying to capture the red in emmission Nebula?
It is suggested on the grey card manufacturers guide sheet that grey card is around 1 to 2 stops darker when imaging at low light.

Any suggestions?

Regards
Carl Rainer