If u spray paint snow black on a sunny but cold day.... Would it melt?

It will melt faster than clean white snow

dark colors absorb heat better than light colors, and white does a very good job of reflecting heat.

Black snow will heat up, and melt faster than cold snow.

It depends on how cold it is and how bright the sun is. Snow melts faster on an asphalt road than on a green lawn just because the asphalt does absorb more of the energy from the sun. But things like time of day (angle of the sun's rays), wind speed (dissipates heat faster) and air temperature all come into play.

It would in fact melt faster than the surrounding white snow but only after temperatures rise above freezing.

In all probability, yes it would. the darker colour would cause the snow to absorb more heat, theoretically making it melt faster.

How about yellow snow?