CAGradientLayer *newShadow = [[CAGradientLayer alloc] init];

    //添加渐变的颜色组合

    newShadow.colors = [NSArray arrayWithObjects:

                        (id)[[[UIColor colorWithRed:236./255. green:240./255. blue:241./255. alpha:1.0] colorWithAlphaComponent:1.0f] CGColor],

                        (id)[[[UIColor colorWithRed:236./255. green:240./255. blue:241./255. alpha:1.0] colorWithAlphaComponent:0.0f] CGColor],

                        nil];

 

    newShadow.colors = [NSArray arrayWithObjects:

                        (id)[[[UIColor colorWithRed:236./255. green:240./255. blue:241./255. alpha:1.0] colorWithAlphaComponent:1.0f] CGColor],

                        (id)[[[UIColor clearColor] colorWithAlphaComponent:0.0f] CGColor],

                        nil];

 

如果只是指定clearColor，无法判断渐变的RGB value，达不到预想颜色。

而指定相同rgb，不同透明度，则可以保证rgb不变，只改变透明度渐变。