I was wondering if this is possible.
what I want is to have my video moving - it starts out as unsaturated (b &w) then as the mask on top moves / expands it brings in the color.

let me give a little more detail.
picture a wedding video... its b & w now as the layer above (for simple purposes - let say its a heart mask) as it grows the area within is now colorized.
BUT you can still see the rest of the video - its just b & w...
can this be done?
let me post this as an example from the Creating Motion graphics with after effects book by Meyer...
http://www.w4cworldwide.com/BT12-DigitalGogh.mov

do you see how there is what looks like an explosion .. and inside the explosion is color and outside of it is color-les.

thanks in advance

Acts7