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