Thanky, I will try, if changing the Material-Name solves the problem, it is ok (yes, sometimes I am too lazy to name the materials properly)
But as you can see in your own example: there are so may greens, some pinks, but no yellows, no oranges. all ID-Pass-colours are pretty close. this will work for a small number of non overlapping objects, but not for a complex scene with 100s of materials. It woulb be nice, if coroa allways provides the widest range of poosible colors.