Monochrome Is Old and Bad; Colored Is New and Good

It's because old movies are in black and white and new movies are in color.

In infomercials and commercials, monochrome color filter represents life before the Advertised Product, meaning that it's bad and whoever somehow managed to live in this time is old-fashioned and living wrong. The colored parts of the infomercial or commercial are when the people in the advertisement have the Advertised Product on their side and are now living life correctly.

Monochrome times also have Idiot Infomercial People who apparently are Complete Screw-Ups and fumble everything and fail at existing. They're so bad at living, they also get a big red X going through them and their home to further show that they're morons who're doing it wrong.