The correct sentence is: The bike on the bike rack is blue.
The other sentences have subject-verb agreement errors:
- "The surface of the parking lots were redone this summer." should be "The surface of the parking lots was redone this summer." (because "surface" is singular).
- "The cars in the parking lot belongs to the teachers." should be "The cars in the parking lot belong to the teachers." (because "cars" is plural).
- "The sidewalks in the courtyards has been decorated with chalk." should be "The sidewalks in the courtyards have been decorated with chalk." (because "sidewalks" is plural).