Imagine that you're a developer at a company that has had a certain shade of red as a part of their branding for the past 134 years. It's a red that's known worldwide.
You pop that color into your iOS app and quickly realize two things:
1) The red you specified is not the red that's displayed.
2) Your brand color is secondary to the chrome that Apple has imposed.
Marketing blows a gasket so you start implementing your own controls: without accessibility, device traits, etc.
Good one, Alan.