DC10 DEP EWR MISUNDERSTOOD CTLR INSTRUCTIONS FOR VECTORS JUST AFTER TKOF.

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WE WERE HVY FOR THE FLT TO AMSTERDAM FROM EWR. DEPARTING RWY 22L WITH THE EWR 6 SID; I BRIEFED THE CAP -- AN IMMEDIATE L TURN TO 190 DEGS WITH A R AT 2.3 DME TO 220 DEGS; CLB TO 2500 FT (ATC RESTR). FLYING THE DEP; ATC ISSUED A L TO 230 DEGS AS WE CROSSED THE 2.3 DME FIX; CLB TO 6000 FT AND A FREQ CHANGE. THE NEXT CTLR; WHO WAS VERY BUSY; ISSUED A 'TIGHT TURN TO 040 DEGS;' WHICH I MISTAKENLY ASSUMED TO BE A L TURN. STARTING THE TURN; ATC COMMENTED 'NEED A NICE TIGHT TURN...' WHICH THE CAPT RESPONDED AFFIRMATIVELY. THEN ATC CAME BACK 'JUST WANTED TO CONFIRM A R TURN.' WE COMPLIED WITH IMMEDIATELY. LOOKING BACK; I SHOULD HAVE REQUESTED CLARIFICATION ON DIRECTION OF TURN. ATC NEVER ISSUES A 'TIGHT TURN...;' ALWAYS A DIRECTION OF TURN -- R TURN IS WHAT HE MUST HAVE SAID. IN THIS SIT; I KNEW THERE WAS PARALLEL DEP OFF OF RWY 22R; AND AT THE TIME THE 040 DEG TURN HDG WAS ISSUED; A L WAS THE CLOSEST DIRECTION. ALSO; I WAS TOO EAGER TO COMPLY INSTANTLY IN A VERY BUSY ENVIRONMENT WITH RAPIDLY ISSUED CLRNCS. NEXT TIME; I WILL BE SLOWER TO REACT AND VERIFY ANY ATC CLRNC THAT SEEMS VAGUE OR NONSTANDARD -- ESPECIALLY ONE AS CRITICAL AS DIRECTION OF TURN THAT CLOSE TO THE ARPT.