The Collaborative International Dictionary of English v.0.48:

Striking \Strik"ing\, a.
   Affecting with strong emotions; surprising; forcible;
   impressive; very noticeable; as, a striking representation or
   image; a striking resemblance. "A striking fact." --De
   Quincey. -- Strik"ing*ly, adv. -- Strik"ing*ness, n.
   [1913 Webster]

WordNet (r) 3.0 (2006):

strikingness
    n 1: the state of being salient [syn: salience, saliency,
         strikingness]
    2: the quality of standing out strongly and distinctly [syn:
       boldness, strikingness]