Change the color of the diagram you want CABasicAnimation to animate

#import<UIKit/UIKit.h>
// No changes.
@ interface ViewController:UIViewController

@end

#import "ViewController.h"
#import "GraphLayer.h"

@ interface ViewController()
// Paste the graphView in the Storyboard.It is recommended that you make it square.
@property(weak, nonatomic)IBOutlet UIView*graphView;
// Instance of GraphLayer.
@property(nonatomic)GraphLayer*graphLayer;

@end

@implementation ViewController

- (void) viewDidLoad{
    superviewDidLoad;

    self.graphLayer=[[GraphLayer alloc] init];
    self.graphLayer.frame = CGRectMake (0.0, 0.0, self.graphView.frame.size.width, self.graphView.frame.size.height);
    // The initial value of the pie chart is 40 percent.
    self.graphLayer.perCent=40.0;
    // The initial color of the pie chart is red. Notice that color information is handled by HSB.
    UIColor*redColor= [UIColorredColor];
    CGFloat theHue;
    [redColor getHue: & theHue saturation: NULL brightness: NULL alpha: NULL];
    self.graphLayer.hue =theHue;
    [self.graphView.layer addSublayer:self.graphLayer];
}
// The action method to start the animation.
- (IBAction) animate: (id) sender {
    CABasicAnimation*graphAnimation=[CABasicAnimation alloc] init];
    graphAnimation.keyPath=@"perCent";
    graphAnimation.fromValue = [NSNumber numberWithFloat:40.0];
    // It shall be 90% after change.
    self.graphLayer.perCent=90.0;
    graphAnimation.toValue = [NSNumber numberWithFloat: 90.0];

    CABasicAnimation*colorAnimation=[CABasicAnimation alloc] init];
    // Change to blue.
    colorAnimation.keyPath=@"hue";
    UIColor*redColor= [UIColorredColor];
    CGFloat redHue;
    [redColor getHue: & redHue saturation: NULL brightness: NULL alpha: NULL];
    colorAnimation.fromValue = [NSNumber numberWithFloat:redHue];
    UIColor*blueColor= [UIColor blueColor];
    CGFloat theHue;
    [blueColor getHue: & theHue saturation: NULL brightness: NULL alpha: NULL];
    self.graphLayer.hue =theHue;
    colorAnimation.toValue = [NSNumber numberWithFloat:theHue];
    // Use the CAAnimationGroup class to perform multiple animations simultaneously.
    CAAnimationGroup*group=[CAAnimationGroup alloc] init];
    group.animations=@[graphAnimation, colorAnimation];
    group.duration=1.0;
    [self.graphLayer addAnimation:group forKey:@"Graph";
}

@end

#import<UIKit/UIKit.h>
// Xcode 6 and iOS 8.x don't need to import the QuartzCore framework.
#import<QuartzCore/QuartzCore.h>

@ interface GraphLayer: CALayer

@property(assign)CGFloat perCent;
Only hue is used as a property, not as a whole color information.
@property(assign)CGFloathue;

@end

#import "GraphLayer.h"

@implementationGraphLayer{
    CGFloat angle;
    CGFloat radius;
    UIColor*fillColor;
}

- (id) init {
    self=[super init];
    if(self){
        // The default value is appropriate.
        angle = 50.0;
        fillColor= [UIColor blackColor];
        // It seems necessary for animation processing.
        self.needsDisplayOnBoundsChange=YES;
        self.contentsScale=[UISscreen mainScreen].scale;
    }
    return self;
}
// It seems necessary for animation processing.
- (id) initWithLayer: (id)layer{
    self=[super initWithLayer:layer];
    if(self){
        self.needsDisplayOnBoundsChange=YES;
        self.contentsScale=[UISscreen mainScreen].scale;
    }
    return self;
}
// Specifies the key corresponding to the keyPath for CABasicAnimation.
+ (BOOL) needsDisplayForKey: (NSString*)key {
    if([key isEqualToString:@"perCent"){
        return YES;
    } else if([key isEqualToString:@"hue"){
        return YES;
    }
    return [super needsDisplayForKey:key];
}
// Drawing process. You can use CGPath instead of CGContext~.
- (void)drawInContext: (CGContextRef)ctx{
    if(self.frame.size.width>=self.frame.size.height){
        radius =self.frame.size.height/2.0;
    } else{
        radius =self.frame.size.width/2.0;
    }
    CGContextMoveToPoint (ctx, radius, radius);
    CGContextAddArc (ctx, radius, radius, radius, radius, M_PI/-2.0, angle-M_PI/2.0, 0);
    CGContextClosePath(ctx);
    CGContextSetFillColorWithColor (ctx, fillColor.CGColor);
    CGContextFillPath(ctx);
}

// Accessor Methods
// Convert percentage to angle.
- (CGFloat)perCent{
    return angle/M_PI*50.0;
}

- (void) setPerCent: (CGFloat) perCent {
    angle = M_PI*perCent/50.0;
}
// Generated UIColor from hue.
- (CGFloat) hue {
    CGFloat theHue;
    [fillColor getHue: & theHue saturation: NULL brightness: NULL alpha: NULL];
    return theHue;
}

- (void)setHue: (CGFloat)hue {
    fillColor=[UIColor alloc] initWithHue: hue saturation: 1.0 brightness: 1.0 alpha: 1.0 ];
}

@end