You're not always in control of the logo's color ! There are many circumstances in which you need a logo to be just white or black or an appropriate color. Think of cut-outs in displays or materials like wood or steel, logos on covered backgrounds, printed logos in just a single choice of ink...

So your logo first needs to be unmistakably clear and recognisable in any rendition, so that's why it's often designed and/or at least tested in black and white ! Then picking a color (or color scheme) is the next and obvious step.

E.g. below, how the colourful idea of a logo turns into a completely different shape when those colors aren't avaliable:

Oorspronkelijk geplaatst op Quora: Do people really think about color theory when designing logos?"