How to get the pixel color on touch?

This is the one I’ve used, and it looks simpler than the methods you’ve tried.

In my custom view class, I have this:

- (void)touchesBegan:(NSSet *)touches withEvent:(UIEvent *)event {
    UITouch *touch = [[event allTouches] anyObject];
    CGPoint loc = [touch locationInView:self];
    self.pickedColor = [self colorOfPoint:loc];
}

colorOfPoint is a method in a category on UIView, with this code:

#import "UIView+ColorOfPoint.h"
#import <QuartzCore/QuartzCore.h>

@implementation UIView (ColorOfPoint)

-(UIColor *) colorOfPoint:(CGPoint)point
    {
    unsigned char pixel[4] = {0};
    CGColorSpaceRef colorSpace = CGColorSpaceCreateDeviceRGB();
    CGContextRef context = CGBitmapContextCreate(pixel,
            1, 1, 8, 4, colorSpace, (CGBitmapInfo)kCGImageAlphaPremultipliedLast);

    CGContextTranslateCTM(context, -point.x, -point.y);

    [self.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;
    }

Don’t forget to import the category into the custom view class and add the QuartzCore framework.

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Trivial note for 2013: cast that last argument as (CGBitmapInfo) to avoid an implicit conversion warning: example here. Hope it helps.