UIColor extension for getting approximate colors. I use this in unit tests sometimes.

ApproximateColorComparison.swift

//: Playground - noun: a place where people can play

import UIKit
import XCTest

extension UIColor {
    private struct Best {
        var color: (color: UIColor, name: String)
        var distance: CGFloat
    }
    
    func nearest() -> (color: UIColor, name: String) {
        let colors: [(color: UIColor, name: String)] = [
            (.black, "black"),
            (.blue, "blue"),
            (.brown, "brown"),
            (.cyan, "cyan"),
            (.gray, "gray"),
            (.green, "green"),
            (.magenta, "magenta"),
            (.orange, "orange"),
            (.purple, "purple"),
            (.red, "red"),
            (.white, "white"),
            (.yellow, "yellow")
        ]
        
        var best = Best(color: colors.first!, distance: CGFloat.greatestFiniteMagnitude)
        for color in colors {
            let distance = self.distance(from: color.color)
            if distance < best.distance {
                best = Best(color: color, distance: distance)
            }
        }
        return best.color
    }
    
    private func distance(from color: UIColor) -> CGFloat {
        var r1: CGFloat = 0
        var g1: CGFloat = 0
        var b1: CGFloat = 0
        var a1: CGFloat = 0
        var r2: CGFloat = 0
        var g2: CGFloat = 0
        var b2: CGFloat = 0
        var a2: CGFloat = 0
        guard getRed(&r1, green: &g1, blue: &b1, alpha: &a1) && color.getRed(&r2, green: &g2, blue: &b2, alpha: &a2) else {
            preconditionFailure("that didn't work")
        }
        
        let redDistance = (r1 - r2) * 0.299
        let greenDistance = (g1 - g2) * 0.587
        let blueDistance = (b1 - b2) * 0.114
        return (redDistance * redDistance) + (greenDistance * greenDistance) + (blueDistance * blueDistance)
    }
}

let color1 = UIColor(red: 1.0, green: 0.74, blue: 0, alpha: 1)
let nearest1 = color1.nearest()
nearest1.color
nearest1.name

let color2 = UIColor(red: 1.0, green: 0.76, blue: 0, alpha: 1)
let nearest2 = color2.nearest()
nearest2.color
nearest2.name