The Collaborative International Dictionary of English v.0.48:

Colorable \Col"or*a*ble\, a.
   Specious; plausible; having an appearance of right or
   justice. "Colorable pretense for infidelity." --Bp.
   Stillingfleet. -- Col"or*a*ble*ness, n. -- Col"or*a*bly,
   adv.
   [1913 Webster]

         Colorable and subtle crimes, that seldom are taken
         within the walk of human justice.        --Hooker.
   [1913 Webster]