how to dynamically recolor a CGGradientRef

I have three CGGradientRef's that I need to be able to dynamically recolor. When I Initialise the CGGradientRef's the first time I get the expected result, but every time I attempt to change the colors nothing happens. Why?

gradient is an instance variable ins a subclass of CALayer:

@interface GradientLayer : CALayer 
{
    CGGradientRef gradient;
    //other stuff   
}
@end

Code:

    if (gradient != NULL)
    {
        CGGradientRelease(gradient);
        gradient = NULL;
    }

    RGBA color[360];
    //set up array
    CGColorSpaceRef rgb = CGColorSpaceCreateD开发者_如何学编程eviceRGB();
    gradient = CGGradientCreateWithColorComponents
    (
    rgb, 
    color,
    NULL,
    sizeof (color) / sizeof (color[0])
    );
    CGColorSpaceRelease(rgb);
    [self setNeedsDisplay];

CGGradientRefs cannot be dynamically colored. To dynamically color a gradient use a CGShadingRef.