示例图

代码

- (UIColor *)transformFromColor:(UIColor*)fromColor toColor:(UIColor *)toColor progress:(CGFloat)progress {

    progress = progress >= 1 ? 1 : progress;
    progress = progress <= 0 ? 0 : progress;

    const CGFloat * fromeComponents = CGColorGetComponents(fromColor.CGColor);
    const CGFloat * toComponents = CGColorGetComponents(toColor.CGColor);

    size_t  fromColorNumber = CGColorGetNumberOfComponents(fromColor.CGColor);
    size_t  toColorNumber = CGColorGetNumberOfComponents(toColor.CGColor);

    if (fromColorNumber == 2) {
        CGFloat white = fromeComponents[0];
        fromColor = [UIColor colorWithRed:white green:white blue:white alpha:1];
        fromeComponents = CGColorGetComponents(fromColor.CGColor);
    }

    if (toColorNumber == 2) {
        CGFloat white = toComponents[0];
        toColor = [UIColor colorWithRed:white green:white blue:white alpha:1];
        toComponents = CGColorGetComponents(toColor.CGColor);
    }

    CGFloat r = fromeComponents[0]*(1 - progress) + toComponents[0]*progress;
    CGFloat g = fromeComponents[1]*(1 - progress) + toComponents[1]*progress;
    CGFloat b = fromeComponents[2]*(1 - progress) + toComponents[2]*progress;

    return [UIColor colorWithRed:r green:g blue:b alpha:1];
}