Following are the guidelines for apron markings according to the IATA Airport Handling Manual:
Double White Line: Do not cross (marks the boundary of the Manoeuvring Area)
Single White Line: Cross with caution
Broken White Line: A roadway centre line
Offset White Broken Line: Do not cross
Solid Single Red Line: Do not cross during aircraft movement, cross with caution when required. The Red Clearance Line is a 60 cm wide uninterrupted red line. It marks the border between the Apron and the Manoeuvring Area. This line should never be crossed by any vehicle other than aircraft or vehicles used for towing and pushback operations.
Recommended colours for Apron markings are:
RED for safety warning
WHITE for traffic/vehicle markings
YELLOW for aircraft movement on aprons, taxiways and runways as per ICAO.