Things Colbert is still afraid of or stressed out by:

Any moving lights, particularly at night. This includes but is not limited to: Laserpens or pointers; flashlights; headlights reflecting on the walls; camera flashes

The sound of my digital camera turning on, presumably because he knows that a flash will result.

New people in the house.

The vet's office, it could be just the smell or sounds, we do not know. None of our other three have any issues with the vet's whatsoever.

Not having a place to hide.

Sleeping uncovered.

Being held.

Sirens, he starts howling with them and heads for cover.

When we go after him to put a leash on him at walk time.

Me.