It is just one of the myths, nothing else.
In general, oil is supposed to change its color. If it does not change its colour even after driving for 7,000 Kms, then it should put one in suspicions and oil may be fake.
I have recently changed engine oil in my car, and its color has slightly changed in even 60~70 Kms of driving after oil change. How come that engine oil's color remained the same after even 7,000 Kms?