At 4 months old, he will change coloration a few times before maturity.
Before a shed, you may notice his skin look more pale/white than usual. Sometimes, you wont even notice until he starts shedding.
If you've only had him for 4 day, he is still not used to his new environment. Imagine if some big creature suddenly took you from your cozy home and dropped you in the middle of a forest. You'd probably be scared at first too.
Patience is key to getting a chameleon to tolerate you. Give him space for a week or two, ignoring him (no eye contact) while cleaning the cage or feeding. Slowly, start spending more time in the same room as his enclosure so he gets used to seeing you around. Eventually, he may not hide anymore. When you notice this, you can try to offer a feeder from your hand. If he doesnt take it, try again the next day.
In my experience, it is difficult to gain a chameleons trust, but easy to lose that trust too.