The correct sentence is:
"The bike on the bike rack is blue."
The other sentences contain grammatical errors:
- "The sidewalks in the courtyards has been decorated with chalk." should be "The sidewalks in the courtyards have been decorated with chalk."
- "The cars in the parking lot belongs to the teachers." should be "The cars in the parking lot belong to the teachers."
- "The surface of the parking lots were redone this summer." should be "The surface of the parking lot was redone this summer." (It's "surface" [singular], so it should match with "was.")