Differnet colours when writing at different speed in 822a

this is my third dvd writer(after a sony and lg) at i was very surprised when i saw the disk once they were copied in my new benq 822a. It has different colours depending of the speed, i mean for example alcohol not all the time in the same disc writes at 4x.

This is the first time i see this on a dvd, cause i remember that in cds usually happens when writing at a speed of 16x or +.

this only happens in benq??