Sun
He was Goku's sun. With hair just as bright as that which the boy had reached out to for so long during his imprisonment. Sanzo definately didn't have the personality that was close to bright, but the Monkey King didn't quite care. As long as he was near his sun, nothing mattered. Some may say it was a childish outlook on things, but it went far deeper than that. Goku belonged to Sanzo, he owed his life to the priest. Just like the plants lived because of the sun. As long as Sanzo shined down upon Goku...everything would be okay.
Author: Thanks to Nimblnymph for betaing this! As she will be all of my other drabbles!