If the monochromatic source in Young's double slit experiment is replaced by white light, then:

When white light is used in YDSE:The path difference at the central point is zero for all wavelengths. Hence, all colors overlap to form a central white bright fringe.For other points, the condition for maxima depends on wavelength ($\lambda$). Since white light has different $\lambda$, fringes of different colors will be formed at different positions. The fringe closest to the center is violet (shorter $\lambda$) and the farthest is red (longer $\lambda$).After a few fringes, the overlap becomes so significant that the pattern disappears into uniform illumination.