Obj-C and SpriteKit - Changing a sprite value that is created randomly

I'm making a game using SpriteKit and Objective-C.

I have four different texture drops (Blue, Green, Orange and Red) that falls down on screen randomly.

In my ANBDropNode class I have this method:

+(instancetype)dropOfType:(ANBDropType)type {

    ANBDropsNode *drop;

    if (type == ANBDropTypeBlue) {
        drop = [self spriteNodeWithImageNamed:@"bluedrop"];
    } else if (type == ANBDropTypeGreen) {
        drop = [self spriteNodeWithImageNamed:@"greendrop"];
    } else if (type == ANBDropTypeOrange) {
        drop = [self spriteNodeWithImageNamed:@"orangedrop"];
    } else if (type == ANBDropTypeRed){
        drop = [self spriteNodeWithImageNamed:@"reddrop"];
    }

    [drop setupPhysicsBody];
    return drop;
}

And in my GamePlayScene these two:

    -(void)addDrops {

        NSUInteger randomDrop = [ANBUtil randomWithMin:0 max:4];

        self.drop = [ANBDropsNode dropOfType:randomDrop];

        float y = self.frame.size.height + self.drop.size.height;
        float x = [ANBUtil randomWithMin:10 + self.drop.size.width
                                     max:self.frame.size.width - self.drop.size.width - 10];
        self.drop.position = CGPointMake(x, y);

        [self addChild:self.drop];
    }

    -(void)update:(NSTimeInterval)currentTime {

        if (self.lastUpdateTimeInterval) {
            self.timeSinceDropAdded += currentTime - self.lastUpdateTimeInterval;
        }

        if (self.timeSinceDropAdded > 1) {
            [self addDrops];
            self.timeSinceDropAdded = 0;
        }

        self.lastUpdateTimeInterval = currentTime;

}

The question is (and it may sound a little dumber, I know): before the drop hits the ground it has already changed it value. If ANBDropNode *drop is a bluedrop, before it hits the ground the method randomly create another drop and change it value for greendrop, for example. But I don't want this behavior. I want the drop to continue with its value until it reaches the ground so I can detect its color in my didBeginContact method.