FLC OF A FOKKER 100 MISHEARS THE DEP CLRNC AND STARTS TURN IN THE WRONG DIRECTION AFTER TKOF. CTLR SEES THE ERROR AND GIVES THEM AN ALERT TO TURN TO THE CORRECT HDG.

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ATC FACILITY: MDW TWR; CHICAGO DEP. LOCATION: RWY 4R MDW AFTER TKOF. FO TKOF MDW RWY 4R NIGHT DEP. TWR CLRED US FOR TKOF AND I HEARD HDG 025 DEGS; SELECTED 025 DEGS IN HDG SELECT. OUR CLRNC WAS THE MIDWAY 4 DEP; WHICH STATES IF YOUR ASSIGNED HDG IS CLOCKWISE FROM 360 DEGS TO 080 DEG TURN; HDG 100 DEGS AFTER TKOF UNTIL 2400 FT. BRIEFED CAPT OF MY INTENTIONS TO COMPLY WITH DEP PROC SINCE ASSIGNED 025 DEG HDG. AFTER TKOF; I STARTED A TURN TO 100 DEGS; BUT TWR INSTRUCTED TURN L HDG 250 DEGS. THAT WAS MY FIRST CLUE TO A POSSIBLE READBACK ERROR. IMMEDIATELY STARTED L TURN TO 250 DEGS WHEN DEP ASKED IF WE WERE IN THE TURN AND MENTIONED THE RESTR TO REMAIN S OF DPA 096 DEG RADIAL. ONBOARD NAVAIDS INDICATED WE REMAINED S OF DPA 096 DEG RADIAL. I WOULD LIKE TO MAKE A RECOMMENDATION: PLEASE REFORMAT THE MIDWAY 4 DEP PAGE. I SUGGEST WE INSERT IN BOLD LETTERS 'ALL RWYS' ABOVE THE INSTRUCTIONS TO REMAIN WITHIN 4 DME. IN A DARK COCKPIT IT IS EASY TO ASSOCIATE THIS INSTRUCTION WITH THE TEXT ASSOCIATED WITH RWY 13L/C/R; RWY 22L/R; RWY 3L/C/R. SUPPLEMENTAL INFO FROM ACN 429463: WE WERE SUPPOSED TO BE HDG 250 DEGS. FO READ BACK 025 DEGS UPON TKOF CLRNC; AND TWR DID NOT CATCH THE ERROR. I WAS BUSY LOOKING DOWN FINAL FOR RWY 4L SINCE A PLANE WAS ON SHORT FINAL AND I WANTED TO MAKE SURE HE WAS LNDG ON THE L; NOT RWY 4R; WHERE WE WERE.