[Tweener] color tween

[Brian Forstat]

Hi, I am trying to tween the color of a MC.

I have this function, but it keeps giving me the following error  
message.

function btnRollOver(whichBtn:MovieClip, theColor:Number,  
duration:Number):Void {
	Tweener.addTween(whichBtn, {_color:theColor, time:duration,  
transition:"linear"});
}

## [Tweener] Error: The property '_color' doesn't seem to be a normal  
object property of [object Object] or a registered special property


What does this mean? I am not even sure where to start looking.

Thanks a lot for any help!