Dragman
I dont believe the tower specifically told the A109 pilot that it was a lear that was "rolling off the runway", the A109 pilot mistakenly thought it was the 737 that the tower were referring to.
As for the colour, a dark grey aircraft in lowering light conditions lined up on a presumably dark runway could be relatively easy to miss, especially if you are looking at a nice big 737, that you have just assumed is the one lining up for takeoff.