https://stackoverflow.com/questions/61942565/compare-two-uicolors-tap-location-in-uiimageview-vs-assets-catalog-color

ViewController.m

//
// Copyright © 2020 Robert Vojta. All rights reserved.
//

#import "ViewController.h"


@interface UIView(ColorAtPoint)

- (UIColor *)colorAt:(CGPoint)point;

@end

@implementation UIView(ColorAtPoint)

- (UIColor *)colorAt:(CGPoint)point {
    UIView *targetOpaqueView = self;

    while (!targetOpaqueView.isOpaque && targetOpaqueView.superview != nil) {
        targetOpaqueView = targetOpaqueView.superview;
    }

    CGPoint targetPoint = [self convertPoint:point toView:targetOpaqueView];

    unsigned char pixel[4] = {0};
    CGColorSpaceRef colorSpace = CGColorSpaceCreateDeviceRGB();
    if (colorSpace == NULL) {
        return nil;
    }

    CGContextRef context = CGBitmapContextCreate(pixel, 1, 1, 8, 4, colorSpace, (CGBitmapInfo)kCGImageAlphaPremultipliedLast);
    if (context == NULL) {
        CGColorSpaceRelease(colorSpace);
        return nil;
    }

    CGContextTranslateCTM(context, -targetPoint.x, -targetPoint.y);
    [targetOpaqueView.layer renderInContext:context];

    CGContextRelease(context);
    CGColorSpaceRelease(colorSpace);

    UIColor *color = [UIColor colorWithRed:pixel[0]/255.0
                                     green:pixel[1]/255.0
                                      blue:pixel[2]/255.0
                                     alpha:pixel[3]/255.0];

    return color;
}

@end



@interface UIColor(ColorSpaceConversion)

- (UIColor *)convertedToColorSpace:(CGColorSpaceRef)colorSpace;
- (UIColor *)convertedToColorSpace:(CGColorSpaceRef)colorSpace inten:(CGColorRenderingIntent)intent;

@end

@implementation UIColor(ColorSpaceConversion)

- (UIColor *)convertedToColorSpace:(CGColorSpaceRef)colorSpace {
    return [self convertedToColorSpace:colorSpace inten:kCGRenderingIntentDefault];
}

- (UIColor *)convertedToColorSpace:(CGColorSpaceRef)colorSpace inten:(CGColorRenderingIntent)intent {
    CGColorRef converted = CGColorCreateCopyByMatchingToColorSpace(colorSpace, intent, self.CGColor, NULL);

    if (converted == NULL) {
        return nil;
    }

    UIColor *color = [[UIColor alloc] initWithCGColor:converted];
    CGColorRelease(converted);
    return color;
}

@end


@interface UIColor(EuclideanDistance)

- (CGFloat)euclideanDistanceTo:(UIColor *)other;

@end

@implementation UIColor(EuclideanDistance)

- (CGFloat)euclideanDistanceTo:(UIColor *)other {
    CIColor *ciColor = [[CIColor alloc] initWithColor:self];
    CIColor *ciColorOther = [[CIColor alloc] initWithColor:other];

    if (ciColor.numberOfComponents != ciColor.numberOfComponents) {
        NSException *exception = [NSException exceptionWithName:NSInvalidArgumentException
                                                         reason:@"Colors differ in numberOfComponents"
                                                       userInfo:nil];
        @throw exception;
    }

    if (ciColor.alpha != 1.0 || ciColorOther.alpha != 1.0) {
        NSException *exception = [NSException exceptionWithName:NSInvalidArgumentException
                                                         reason:@"Transparent colors are not supported"
                                                       userInfo:nil];
        @throw exception;
    }

    CGFloat dr = ciColorOther.red - ciColor.red;
    CGFloat dg = ciColorOther.green - ciColor.green;
    CGFloat db = ciColorOther.blue - ciColor.blue;

    return sqrt(dr * dr + dg * dg + db * db);
}

@end


@interface UIColor(Matching)

- (BOOL)matchesTo:(UIColor *)other;
- (BOOL)matchesTo:(UIColor *)other euclideanDistanceTolerance:(CGFloat)tolerance;

@end

@implementation UIColor(Matching)

- (BOOL)matchesTo:(UIColor *)other {
    return [self matchesTo:other euclideanDistanceTolerance:0.01];
}

- (BOOL)matchesTo:(UIColor *)other euclideanDistanceTolerance:(CGFloat)tolerance {
    CGFloat distance = [self euclideanDistanceTo:other];
    return distance <= tolerance;
}

@end


@interface ViewController ()

@property (nonatomic, strong) IBOutlet UIImageView *imageView;
@property (nonatomic, strong) IBOutlet UIView *leftView;
@property (nonatomic, strong) IBOutlet UIView *rightView;

@end

@implementation ViewController

- (IBAction)handleTapGesture:(UITapGestureRecognizer *)sender {
    CGPoint location = [sender locationInView:self.imageView];

    CGColorSpaceRef colorSpace = CGColorSpaceCreateWithName(kCGColorSpaceDisplayP3);
    if (colorSpace == NULL) {
        return;
    }

    UIColor *assetsCatalogRedColor = [UIColor colorNamed:@"CustomRedColor"];
    UIColor *redColor = [assetsCatalogRedColor convertedToColorSpace:colorSpace];
    UIColor *tappedColor = [[self.imageView colorAt:location] convertedToColorSpace:colorSpace];

    CGColorSpaceRelease(colorSpace);

    self.leftView.backgroundColor = tappedColor;
    self.rightView.backgroundColor = redColor;

    if (redColor == nil || tappedColor == nil) {
        return;
    }

    @try {
        BOOL matches = [tappedColor matchesTo:redColor];
        NSLog(@"Tapped color matches CustomRedColor: %@", matches ? @"true" : @"false");
    }
    @catch (NSException *exception) {
        NSLog(@"Something went wrong: %@", exception);
    }
}

@end

ViewController.swift

//
// Copyright © 2020 Robert Vojta. All rights reserved.
//

import UIKit
import CoreGraphics

extension UIView {
    func color(at point: CGPoint) -> UIColor? {
        var targetOpaqueView: UIView = self

        // Traverse the view hierarchy to find a parent which is opaque
        while !targetOpaqueView.isOpaque && targetOpaqueView.superview != nil {
            targetOpaqueView = targetOpaqueView.superview!
        }

        // Convert the point from our view to the target one
        let targetPoint: CGPoint = convert(point, to: targetOpaqueView)

        let colorSpace = CGColorSpaceCreateDeviceRGB()
        let bitmapInfo = CGBitmapInfo(rawValue: CGImageAlphaInfo.premultipliedLast.rawValue)
        var pixel: [UInt8] = [0, 0, 0, 0]

        guard let context = CGContext(data: &pixel, width: 1, height: 1, bitsPerComponent: 8, bytesPerRow: 4, space: colorSpace, bitmapInfo: bitmapInfo.rawValue) else {
            return nil
        }

        context.translateBy(x: -targetPoint.x, y: -targetPoint.y)

        // Render the target opaque view to get all the possible transparency right
        targetOpaqueView.layer.render(in: context)
        return UIColor(red: CGFloat(pixel[0])/255.0, green: CGFloat(pixel[1])/255.0, blue: CGFloat(pixel[2])/255.0, alpha: CGFloat(pixel[3])/255.0)
    }
}

extension UIColor {
    func converted(toColorSpace colorSpace: CGColorSpace, intent: CGColorRenderingIntent = .defaultIntent) -> UIColor? {
        guard let converted = cgColor.converted(to: colorSpace, intent: intent, options: nil) else {
            return nil
        }

        return UIColor(cgColor: converted)
    }
}

extension UIColor {
    func euclideanDistance(to other: UIColor) -> CGFloat? {
        let ciColor = CIColor(color: self)
        let ciColorOther = CIColor(color: other)

        guard ciColor.numberOfComponents == ciColorOther.numberOfComponents,
            ciColor.alpha == 1.0, ciColorOther.alpha == 1.0 else {
                return nil;
        }

        let dr = ciColorOther.red - ciColor.red
        let dg = ciColorOther.green - ciColor.green
        let db = ciColorOther.blue - ciColor.blue

        return sqrt(dr * dr + dg * dg + db * db)
    }
}

extension UIColor {
    func matches(to other: UIColor, euclideanDistanceTolerance tolerance: CGFloat = 0.01) -> Bool? {
        guard let distance = euclideanDistance(to: other) else {
            return nil
        }

        return distance <= tolerance
    }
}

class ViewController: UIViewController {
    @IBOutlet var imageView: UIImageView!
    @IBOutlet var leftView: UIView!
    @IBOutlet var rightView: UIView!

    private let assetsCatalogRedColor: UIColor = UIColor(named: "CustomRedColor")!

    @IBAction
    func handleTap(sender: UITapGestureRecognizer) {
        let location = sender.location(in: imageView)

        guard let colorSpace = CGColorSpace(name: CGColorSpace.displayP3),
            let redColor = assetsCatalogRedColor.converted(toColorSpace: colorSpace, intent: .defaultIntent),
            let tappedColor = imageView.color(at: location)?.converted(toColorSpace: colorSpace, intent: .defaultIntent) else {
                return
        }

        let matches = tappedColor.matches(to: redColor) ?? false

        print("Tapped color matches CustomRedColor: \(matches)")

        leftView.backgroundColor = tappedColor
        rightView.backgroundColor = redColor
    }
}