UIImage color changing?

One way to accomplish this is to desaturate your image, and add a tint on top of that image with the color you desire.

Desaturate

-(UIImage *) getImageWithUnsaturatedPixelsOfImage:(UIImage *)image {
    const int RED = 1, GREEN = 2, BLUE = 3;

    CGRect imageRect = CGRectMake(0, 0, image.size.width*2, image.size.height*2);

    int width = imageRect.size.width, height = imageRect.size.height;

    uint32_t * pixels = (uint32_t *) malloc(width*height*sizeof(uint32_t));
    memset(pixels, 0, width * height * sizeof(uint32_t));

    CGColorSpaceRef colorSpace = CGColorSpaceCreateDeviceRGB();
    CGContextRef context = CGBitmapContextCreate(pixels, width, height, 8, width * sizeof(uint32_t), colorSpace, kCGBitmapByteOrder32Little | kCGImageAlphaPremultipliedLast);

    CGContextDrawImage(context, CGRectMake(0, 0, width, height), [image CGImage]);

    for(int y = 0; y < height; y++) {
        for(int x = 0; x < width; x++) {
            uint8_t * rgbaPixel = (uint8_t *) &pixels[y*width+x];
            uint32_t gray = (0.3*rgbaPixel[RED]+0.59*rgbaPixel[GREEN]+0.11*rgbaPixel[BLUE]);

            rgbaPixel[RED] = gray;
            rgbaPixel[GREEN] = gray;
            rgbaPixel[BLUE] = gray;
        }
    }

    CGImageRef newImage = CGBitmapContextCreateImage(context);

    CGContextRelease(context);
    CGColorSpaceRelease(colorSpace);
    free(pixels);

    UIImage * resultUIImage = [UIImage imageWithCGImage:newImage scale:2 orientation:0];
    CGImageRelease(newImage);

    return resultUIImage;
}

Overlay With Color

-(UIImage *) getImageWithTintedColor:(UIImage *)image withTint:(UIColor *)color withIntensity:(float)alpha {
    CGSize size = image.size;

    UIGraphicsBeginImageContextWithOptions(size, FALSE, 2);
    CGContextRef context = UIGraphicsGetCurrentContext();

    [image drawAtPoint:CGPointZero blendMode:kCGBlendModeNormal alpha:1.0];

    CGContextSetFillColorWithColor(context, color.CGColor);
    CGContextSetBlendMode(context, kCGBlendModeOverlay);
    CGContextSetAlpha(context, alpha);

    CGContextFillRect(UIGraphicsGetCurrentContext(), CGRectMake(CGPointZero.x, CGPointZero.y, image.size.width, image.size.height));

    UIImage * tintedImage = UIGraphicsGetImageFromCurrentImageContext();
    UIGraphicsEndImageContext();

    return tintedImage;
}

How-To

//For a UIImageView
yourImageView.image = [self getImageWithUnsaturatedPixelsOfImage:yourImageView.image];
yourImageView.image = [atom getImageWithTintedColor:yourImageView.image withTint:[UIColor redColor] withIntensity:0.7];

//For a UIImage
yourImage = [self getImageWithUnsaturatedPixelsOfImage:yourImage];
yourImage = [atom getImageWithTintedColor:yourImageView.image withTint:[UIColor redColor] withIntensity:0.7];

You can change the color of the tint to whatever you desire.

Check out my post (mostly just remixing code).

Edit: This code basically creates a new CGContext, draws a layer on it with the new color, and returns a new UIImage from that. I haven't gone in depth on this code in a while, but it seems to just draw a UIImage with the same shape as the original, so that's a limit (loses any detail in the image).

Hmmm -- isn't the order of the bytes supposed to be RGBA? You are setting them as ARGB...