[css3-animations] invalid values in keyframes

What should this animation look like?

@keyframes anim1 {
                0% {color: red; left: 10px;}
                50% { color: notARealColor; left: 20px; }
                100% { color: yellow; left: 90px; }
}

Should the specified color property value at 50% effectively be ignored as if it were not specified? Or should the whole animation of the color property be ignored? Or, taking it to a further extreme, should the entire animation be ignored?

It seems more natural to just ignore the specified color value. However, preventing some of the animation from running would be a clear indicator to a web author that there's a problem with his defined animation.