Animating Lights or Textures?

[Legend of Jesse]

basically im working on a stage that calls for the stage (not characters) to be black and white when the match starts... then fades into color... this a lighting effect correct? i have a light setting that i like (for the color part) but i'm not sure how to get the color setting right for a grey scale everything... and then how to fade from the grey scale to the color setting i have now... any suggestions...help... advise... info whatsoever?

if this is not a lighting effect... then is it a texture animation? how do those even work?