B737 CREW CONFUSED RWY 26R FOR RWY 26L AND LINED UP ON RWY 26R FOR TKOF.

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CLRED TO TAXI S; CROSS RWY 26 THRESHOLD; TKOF RWY 26L. AS I REACHED THE S EDGE OF RWY 26 AND LOOKED AHEAD TO RWY 26L; I MISTOOK IT FOR THE PARALLEL TXWY. I TURNED SHARPLY TO LINE UP ON WHAT I NOW THOUGHT WAS RWY 26L. THE FO IMMEDIATELY STATED WE WERE ON RWY 26R. I DIRECTED THE FO TO INFORM TWR WE WERE EXITING RWY 26R TO THE N SIDE. CTLR STATED NO HARM; NO FOUL. DARKNESS WAS A FACTOR IN IDENTING RWYS/TXWYS. ALSO; SOME ARPTS I TRANSIT HAVE THE 'NEW' IN-TXWY AMBER LIGHTS ACROSS THE TXWY TO FURTHER IDENT/LOCATE A RWY HOLD SHORT LINE RWY 26L DOES NOT. THE ABSENCE OF THOSE LIGHTS WAS NOT SO MUCH THE FACTOR AS THE FACT THAT IT LOOKED 'DIFFERENT.' IE; IF NO ARPT HAD THOSE LIGHTS; THEN I MAY HAVE BEEN MORE INCLINED TO LOOK OUT AHEAD AND LOOK FOR A RWY (RWY 26L). BUT SINCE AT SOME ARPTS WHEN YOU DON'T SEE THE AMBER LIGHTS; IT MEANS THERE IS NO RWY THRESHOLD THERE; I SUDDENLY THOUGHT I HAD PASSED ALL RWYS. SUPPLEMENTAL INFO FROM ACN #566436: CLRED TO TAXI ACROSS RWY 26R TO RWY 26L WHILE XING RWY 26R; SOME CONFUSION ENSUED AS TO WHAT RWY WE WERE CLRED ONTO. I ASKED THE TWR IF WE WERE CLRED FOR TKOF ON RWY 26R; AND HE STATED 'YOU BETTER HURRY.' WE DID NOT FEEL THIS CLARIFIED OUR INSTRUCTIONS SO WE EXITED THE RWY IMMEDIATELY AND GOT BACK IN LINE FOR TKOF. THE CTLR SAID; 'NO HARM; NO FOUL.