Circadian clocks regulate the physiology and behavior of most animals. Drosophila melanogaster mutants helped more than any other animal in understanding these timing mechanisms. This study aims to investigate the effect of the yellow white (y w) mutation on circadian behavior of D. melanogaster flies under rhythmic cycles of light-dark (LD), constant dark (DD) and continuous light (LL) conditions. These mutant flies suffer from disturbances in eye and body pigmentation in addition to altered neural development and behavioral control, making them good candidates for investigating the function of the circadian clock. The obtained results indicated that y w mutants are rhythmic in LD conditions, with significantly higher daytime activity compared to control wild-type Canton S (CS) flies. In constant conditions, they free run in DD with a significantly shorter periodicity (Tau) (τ=23.82, SD=0.44) compared to (τ=24.59, SD=0.39) in CS, indicating a faster endogenous clock in DD, while they were arrhythmic in LL as expected, similar to CS flies. Mutant y w flies also exhibited a crepuscular activity pattern with two peaks of activity. The y w flies' morning peak was significantly delayed by about 2.5 hours, but ending at the same time in both groups. The evening peak was significantly advanced by about 1.7 hours. This resulted in a significant shortening of midday siesta by about 1.5 hours compared to CS flies. Collectively, these changes resulted in a significant shift of activity towards the light-phase in the mutant y w flies. Moreover, morning anticipation of these flies was slightly reduced and did not integrate smoothly into the morning peak. It is possible to conclude that the altered pigmentation and neuronal development in y w mutants has a profound effect on circadian organization of locomotor activity. These results provide new insights for a better understanding of behaviors studied in the y w genetic background.