SKAction+FadeColorAction.h

//
//  SKAction+FadeColorAction.h
//

#import <SpriteKit/SpriteKit.h>

@interface SKAction (FadeColorAction)

+ (SKAction*) fadeColorFrom:(SKColor*)fromColor toColor:(SKColor*)toColor duration:(CGFloat)duration;

@end

SKAction+FadeColorAction.m

//
//  SKAction+FadeColorAction.m
//

#import "SKAction+FadeColorAction.h"

// Note: It's probably best to relocate this to whereever you typically define macros
#define lerp(a, b, fraction) ((((b) - (a)) * (fraction)) + (a))

@implementation SKAction (FadeColorAction)

// Modified from: http://stackoverflow.com/a/27825008/522498
+ (SKAction*) fadeColorFrom:(SKColor*)fromColor toColor:(SKColor*)toColor duration:(CGFloat)duration {
    
    // get the Color components of col1 and col2
    CGFloat r1 = 0.0, g1 = 0.0, b1 = 0.0, a1 = 0.0;
    CGFloat r2 = 0.0, g2 = 0.0, b2 = 0.0, a2 = 0.0;
    [fromColor getRed:&r1 green:&g1 blue:&b1 alpha:&a1];
    [toColor getRed:&r2 green:&g2 blue:&b2 alpha:&a2];
    
    return [SKAction customActionWithDuration:duration actionBlock:^(SKNode *node, CGFloat elapsedTime) {
        
        CGFloat fraction = elapsedTime / duration;
        
        SKColor *interpolatedColor = [SKColor colorWithRed:lerp(r1,r2,fraction)
                                                     green:lerp(g1,g2,fraction)
                                                      blue:lerp(b1,b2,fraction)
                                                     alpha:lerp(a1,a2,fraction)];
        
        [(SKShapeNode*)node setFillColor:interpolatedColor];
        [(SKShapeNode*)node setStrokeColor:interpolatedColor];
    }];
}

@end