These are High Capacity Parcel Vans from different zonal railways, thus being of diff colours. Nowadays IR runs a special freight service called 'Speed Link Express', which is considerably faster than goods trains. These trains consist of such coaches with 1 SLR / DSLR for guard. Besides, they are often attached to long distance SF / M / E trains like, 12629 / 30 K'taka SK, 12345/46 Saraighat Exp etc.