How can we use Assets Catalog Color Sets?

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

As @Cœur says we can drag&drop de color, and use it like a UIColor object and a possible solution could be use it as a extension:

Or as a constant:

Now I wanna know if we can access them like an UIImage access to an Asset Image or not, like:

UIImage(named: "image-name") -> UIColor(named: "color-name")

UIColor(named: "myColor") 

Source: WWDC 2017 Session 237 —— What's New in MapKit

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Caveat: Your project's Deployment Target needs to be set to iOS 11.0.

(short answer to the question update: there is UIColor(named: "MyColor") in Xcode 9.0)

Answering the original question:

1. you create your color set

2. you find your color among your snippets and you drag-n-drop it

3. 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.

In Xcode 11 press command + shift + L , it will open a snippet , select last one like i showed in image drag and drop .

Short Version

Add a colour set to an asset catalog, name it and set your colour in the attributes inspector, then call it in your code with UIColor(named: "MyColor").

Full Instructions

1. In the asset catalog viewer, click the plus button at the bottom right of the main panel and choose New Color Set

   

2. Click on the white square, and select the Attributes Inspector (right-most icon in the right pane)

3. From there you can name and choose your colour.

   

4. To use it in your code, call it with UIColor(named: "MyColor"). This returns an optional, so you'll need to unwrap it in most cases (this is probably one of the few cases where a force unwrap is acceptable, given you know the colour exists in your asset catalog).

You need to use UIColor(named: "appBlue").

And you can create a function in UIColor extension for simple access.

enum AssetsColor {
   case yellow
   case black
   case blue
   case gray
   case green
   case lightGray
   case separatorColor
   case red
}

extension UIColor {

    static func appColor(_ name: AssetsColor) -> UIColor? {
        switch name {
        case .yellow:
            return UIColor(named: "appYellow")
        case .black:
            return UIColor(named: "appBlack")
        case .blue:
            return UIColor(named: "appBlue")
        case .gray:
            return UIColor(named: "appGray")
        case .lightGray:
            return UIColor(named: "appLightGray")
        case .red:
            return UIColor(named: "appRed")
        case .separatorColor:
            return UIColor(named: "appSeparatorColor")
        case .green:
            return UIColor(named: "appGreen") 
        }
    }
}

You can use it like this:

userNameTextField.textColor = UIColor.appColor(.gray)

You can use this way for simple accessing (swift 4 & swift 5)

enum AssetsColor: String {
    case backgroundGray
    case blue
    case colorAccent
    case colorPrimary
    case darkBlue
    case yellow
}

extension UIColor {
    static func appColor(_ name: AssetsColor) -> UIColor? {
         return UIColor(named: name.rawValue)
    }
}

Using:

userNameTextField.textColor = UIColor.appColor(.blue)

 // iOS
 let color = UIColor(named: "SillyBlue")

 // macOS
 let color = NSColor(named: "SillyBlue")

For your question if you can access color assets like the image using literal, as of Xcode 10.2 you can type in colorliteral, then you can pick the color you want to use that is under your asset manager.

In case you experience a delay with colors loading in a Swift Package when using UIColor(named:):

The answers above are totally valid for a regular project but if you are using assets in a swift package, you can see a delay when loading the colors when you use UIColor(named: "example_name"). If you use UIColor(named: "background", in: Bundle.module, compatibleWith: .current) overload that is targeting the module, the colors load immediately without any delay.

Note: I experienced this on Xcode 12.1.

for swiftUI create a class and name it : Color+extansion and extend Color :

import SwiftUI

extension Color {
    static let background = Color("BackgroundColor")
    static let whiteColor = Color("WhiteColor")
    static let blackColor = Color("BackgroundColor")
    static let primery = Color("PrimeryColor")
    static let secondaryColor = Color("SecondaryColor")    
}

Or, with the SwiftUI Color structure, you can simply call the initializer with the asset name:

Color("background")