#import <UIKit/UIKit.h>

@interface TwoViewController : UIViewController

@property (nonatomic,copy)void(^_changeColorBlock)(UIColor *);


@end

#import "TwoViewController.h"
 - (IBAction)goto1:(UIButton *)sender {

    UIColor *color = sender.tag == 1?[UIColor redColor]:sender.tag == 2?[UIColor greenColor]:[UIColor blueColor];
    __changeColorBlock(color); 
    [self.navigationController popViewControllerAnimated:YES];
}
#import "OneViewController.h"
- (IBAction)goto2:(id)sender {
    TwoViewController *vc = [[TwoViewController alloc]init];
    void (^block)(UIColor *) = ^(UIColor *color){
        self.view.backgroundColor = color;
    };
    vc._changeColorBlock = block;
   [self.navigationController pushViewController:vc animated:YES];
}