Flat Color Rules
So many companies that had either multicolored logos or logos that required gradients or a halftone screen have realized that there are just too many situations where their identities did not reproduce properly or clearly or without extra expense. From vehicles (where printed vinyl doesn’t last as long) to stationery (which is often printed on smaller presses) to the separate issue of basic clarity.
Many companies have changed their logos to work in one flat color (which means, of course, that they could work in solid black as well).
With many of these examples, issues other than color are also addressed to good effect.
It might seem counter-intuitive to the inexperienced, but a single flat color is inherently clearer than any multicolored variation.
Adapted from Logo Design Theory: How Branding Design Really Works