What was found
RETURNED TO IAD DUE TO MULTIPLE NAVIGATIONAL DISPLAY PROBLEMS. CAPT & F/O ADI'S WERE LOSING COLOR & BLANKING. DURING IN-FLIGHT TROUBLESHOOT CREW ALSO NOTED CONFIG LIGHT AND GEAR NOT DOWN MESSAGE. AS A RESULT, 4 LRU'S WERE REMOVED:CAPT. ADI, CENTER SG, LANDING CONFIG WARNING CARD AND RAD ALT XCVR. ADI HAD EVIDENCE OF DIRT BUILD-UP, WHICH MAY HAVE CAUSED OVERHEAT CONDITION. SG AND WARNING CARD WERE NFF. RAD ALT XCVR NEEDED 2 CCOA'S & FAILED TX FREQ & SELF TEST. A/C HAS NOT EXPERIENCED SIMILAR PROBLEMS SINCE INCIDENT.