How to specify instance mask in coco panoptic annotation format?

[zeng-hello-world]

Here is a coco panoptic segmentation annatation format from COCO website:

Since the segment_info has only category_id related to instance color mask in annotation mask image, how do you tell instances have the same category_id one from another?

Also, I noticed panoptic annotation mask images in this project: sample_data/panoptic_examples/000000142238.png

the color of these person category are a little different from each others.

Thanks!