Convert an HTML-style web hexadecimal color string to a UIColour instance. See also C# version.

README-UIColourExtension.md

Swift 5.0

Swift 5.0 cannot use the #ffffff syntax directly. Here is the code I use for web-related projects. Supports alpha and three-digits.

Usage example (uppercase values are fine too):

    let hex = "#FADE2B"  // yellow
    let color = UIColor(fromHex: hex)

Supported string formats:

• "fff" // RGB
• "#fff" // #RGB
• "ffff" // RGBA
• "#ffff" // #RGBA
• "ffffff" // RRGGBB
• "#ffffff" // #RRGGBB
• "ffffffff" // RRGGBBAA
• "#ffffffff" // #RRGGBBAA

The digits represent Red, Green, Blue and Alpha (like transparency).

IMPORTANT

This is written for iOS (UIKit). For MacOS (AppKit), replace UIColor with NSColor.

Alternatives:

You can remove the # and store it as a 32-bit unsigned integer literal, denoted by a 0x prefix thus: 0xffffff. You still need code to convert this to a colour though.

If you're wanting a non-programatic way to get the color: Open a colour selector dialog and switch to Colour Sliders > RGB Sliders and paste/enter the value into the 'Hex Color #' box. (Don't paste the # hash symbol.)

Caveat:

Hex colours originating from Android are usually in format AARRGGBB and will thus require reformatting. e.g. let newColor = color.suffix(6).prefix(4) + color.prefix(2)

Source:

https://gist.github.com/akingdom/75778998e0d435060d645c0be35f9c24

UIColorExtension.swift

// Swift 5.0
// Color from a web-style hex string
//
// By Andrew Kingdom
// MIT license
// 
extension UIColor {
    /// Initialises UIColor from a hexadecimal string. Color is clear if string is invalid.
    /// - Parameter fromHex: supported formats are "#RGB", "#RGBA", "#RRGGBB", "#RRGGBBAA", with or without the # character
    public convenience init(fromHex:String) {
        var r = 0, g = 0, b = 0, a = 255
        let offset = fromHex.hasPrefix("#") ? 1 : 0
        let ch = fromHex.map{$0}
        switch(ch.count - offset) {
        case 8:
            a = 16 * (ch[offset+6].hexDigitValue ?? 0) + (ch[offset+7].hexDigitValue ?? 0)
            fallthrough
        case 6:
            r = 16 * (ch[offset+0].hexDigitValue ?? 0) + (ch[offset+1].hexDigitValue ?? 0)
            g = 16 * (ch[offset+2].hexDigitValue ?? 0) + (ch[offset+3].hexDigitValue ?? 0)
            b = 16 * (ch[offset+4].hexDigitValue ?? 0) + (ch[offset+5].hexDigitValue ?? 0)
            break
        case 4:
            a = 16 * (ch[offset+3].hexDigitValue ?? 0) + (ch[offset+3].hexDigitValue ?? 0)
            fallthrough
        case 3:  // Three digit #0D3 is the same as six digit #00DD33
            r = 16 * (ch[offset+0].hexDigitValue ?? 0) + (ch[offset+0].hexDigitValue ?? 0)
            g = 16 * (ch[offset+1].hexDigitValue ?? 0) + (ch[offset+1].hexDigitValue ?? 0)
            b = 16 * (ch[offset+2].hexDigitValue ?? 0) + (ch[offset+2].hexDigitValue ?? 0)
            break
        default:
            a = 0
            break
        }
        self.init(red: CGFloat(r)/255, green: CGFloat(g)/255, blue: CGFloat(b)/255, alpha: CGFloat(a)/255)
        
    }
}

See https://stackoverflow.com/a/63443672/1419960 for details.