Motorman,

 Just clean up the part for fitment (if necessary) as you normally would and don't worry about the brown. If you're happy with the part fit as is you can simply wipe along the brown edge with your finger to remove any loose residue that might be there and then get out the glue. Sometimes though you'll notice that the edge is not perfectly square or flat as it comes out of the sheet. Because of that I'll always give any laser cut part at least a good close look and a light scuff with some fine sandpaper just to make it "perfect", just depends how picky one wants to get.

Do you have to sand all the brown off the balsa before you glue it? I messes up the fit of the parts when you do.

AS said  just glue it, the brown hurts nothing, and may actually improve the joint when using CA

Randy

I'd paint any exposed edges black and tell the inquisitive that it's CF strip... Steve

If one plans to use the transparent films, a light cleaning/sanding will clear the cinched balsa. It looks very ugly when finished.
No problems on gluing.