OK...technically speaking...color is simply the reflection of light in different frequencies of the spectrum. Black objects are absorbing all light and therefore do not reflect any light/colors. White objects are reflecting all light/colors. So when you look at an object that is seen as a specific color, you are actually seeing the only color that it is not absorbing.
So in truth, calling one the absence of light/color and the other the blending of all light/color is simple matter of perspective. Are you referring to what is absorbed or what is reflected.
The reason I choose to say that white is a mixture of all colors is because when you perform the simple test of spinning a color wheel, it turns white, not black. And, when we refer to a color, it is commonly accepted that the color reflected is the color of the object.
So...in conclusion...if we want to say that white is the absence of color, we have to call a car the we see as red to actually be every color but red.
Or maybe I have it all wrong.