I usually use custom UIColors on iOS using extensions with Swift, but now with iOS 11/ Xcode 9 we can create Colors Sets. How can we use them?
Update - Tip>
(short answer to the question update: there is UIColor(named: "MyColor") in Xcode 9.0)
Answering the original question:
it will translate to a color literal when looking at the source code:
#colorLiteral(red: 0, green: 0.6378085017, blue: 0.8846047521, alpha: 1)
You notice how the values of red, green and blue are different? It's because I defined them using Color Space Display P3, but the colorLiteral is using Color Space sRGB.