As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
F/O`S FMC CDU HAS A PURPLE LINE ON THE RT SIDE. ACFT GROUNDED. ON INITIAL POWER UP NO PURPLE LINE WAS VISIBLE. WHEN SCREEN WAS TOUCHED, SEVERAL PURPLE LINES APPEARED AND SCREEN WAS DISTORTED. REPLACED FMC CDU, ALL OPS NORMAL, REF AMM 34-61-01.