German WWII aircraft crosshairs were typically black or dark gray, as they were simple metal or etched glass reticles without illumination. However, later in the war, advanced gunsights like the Revi (Reflexvisier) series introduced an illuminated reticle that appeared red, orange, or yellow against the glass, improving visibility in low-light conditions. Fighters like the Bf 109 and Fw 190 used the Revi 16B and 16C, which projected a red/orange aiming reticle, making target tracking easier. Some night fighters, like the Bf 110, had adjustable brightness for better visibility.
Sometimes I find it hard to see the yellowish aiming reticle. If red could be added that would be a great improvement.