ALTDEV DURING CLBOUT.

Narrative

FLT FROM MCI TO EWR. ON CLBOUT OF MCI; WHILE CLRED TO 15000 FT; I DID NOT HEAR THE FO AS HE RECEIVED THE CLRNC TO WHAT HE THOUGHT WAS FL330. AS WE CLBED THROUGH FL230; THE CTLR SAID MAINTAIN FL230. I IMMEDIATELY DSNDED BACK TO FL230; THE CTLR THEN ASKED IF WE WERE ASSIGNED A DIFFERENT ALT AS SHE HAD JUST COME ON THE SCOPE. WE TOLD HER THAT WE BELIEVED THAT WE WERE CLRED TO FL330. WE ASKED IF THERE WAS A PROB AND SHE SAID THAT THEY WOULD HAVE TO LISTEN TO THE TAPES. AFTER LNDG AT EWR; I CALLED THE CTR AND THEY SAID THAT THE TAPES WERE VERY SCRATCHY BUT THEY BELIEVED THAT WE READ BACK FL230. THEY VERIFIED THAT THERE WAS NO LOSS OF SEPARATION BUT BY THIS TIME THE RPT HAD BEEN FILED. DURING THIS TIME FRAME; 18000 FT TO FL230; A FLT ATTENDANT CAME TO THE FLT DECK TO TAKE DRINK ORDERS; WHICH IS CUSTOMARY. THIS COULD HAVE CONTRIBUTED TO THE PROB. SO NOW I DON'T TURN OFF THE STERILE FLT DECK LIGHT UNTIL WE HAVE BEEN CLRED ABOVE FL230 AND HAVE RECEIVED THE CRUISE ALT CLRNC. ALSO; EVERY ALT CLRNC IS NOW VERBALLY REPEATED BY BOTH PLTS. SUPPLEMENTAL INFO FROM ACN 277098: SOMETHING ELSE I NOTICED ON THE ADVANCED 737'S; IS THAT THE MODE CTL PANEL; WHICH HAS HDG; COURSE; AND ALT INFO IS DONE WITH A GRAY LIQUID CRYSTAL DISPLAY ON A BLACK BACKGND; WHICH IS EXTREMELY DIFFICULT TO SEE ON A SUNNY DAY.