That looks like a bug in the original engine, not Maelstrom; Maelstrom does it correctly. The texture is an alpha mask, with no color, so it will take the shade of color sent to the engine from the Crosshair colors.
If you look at SEA_AI\AICameras.c for COAS, these are the colors:
Crosshair.Colors.Default = argb(0, 255, 255, 255);
Crosshair.Colors.Enemy = argb(0, 255, 0, 0);
Crosshair.Colors.Friend = argb(0, 0, 255, 0);
Crosshair.Colors.Neutral = argb(0, 128, 128, 128);
If you want the Default to be Yellow, change this line:
Crosshair.Colors.Default = argb(0, 255, 255, 255); //For Yellow, change it to argb(0, 255, 255, 0)