In my book of waves and optics, there's a chapter about the rings of Newton and as a question there is: how is the interference pattern when we use white light, considering me it's : there are rings in different color, the ring with the smallest diameter is in blue. But then they ask what's the difference with spectral light and I don't really know this.
"Spectral light" is a fairly weird phrasing, but presumably it means monochromatic light of well-defined wavelength. This will produce a well-defined set of rings.
White light, by comparison, is formed by multiple wavelengths, all of which will create rings at different diameters, overlapping with each other. At the very center, you'll be able to observe some interference, with light and dark fringes separated by coloured boundaries (caused by the different spacings of the different colours), but these will quickly wash out and the interference will be destroyed as dark fringes in one colour start to overlap completely with light fringes in other colours.