I aggree with the idea would be real nice
I also can see why it doent exist right now, becuase the lines from the source window dont actually contain a color, but were only colored that way in that window, not in the new one. (not that i think that behavour is the best at all, just why it happens)

On the same grounds as you would like to see the color hold when filtered etc, I would like to be able to just sample what it is, as that ability is missing also.
ie:

//window @x | aline $rand(0,15) @x a random color

Now how do i find out what color it was?!?!?!