(1) Scattering concerns the interaction of light with particles. For example, there is scattering of light by the atmosphere. Light is also scattered during reflection when the light penetrates the surface, bounces around under the surface and then eventually leaves the surface again.
(2) Generally light does not change its wavelength when it falls on a rough surface. There are fluorescent materials that absorb light at one wavelength and re-emit it at another, but this doesn't have to do with surface roughness. What surfaces other than white ones do is absorb different amounts of light at different wavelengths, which leads to surfaces colours. The relative amounts that a surface reflects at different wavelengths is called its percent surface spectral reflectance.