This is the first time I've noticed this happen. My truck had sat for 2 days, and when I started it up yesterday blue and white smoke puffed out for a second.
What would be the cause of this?

 

It's usually caused by worn valve seals, which let a small amount of oil into the cylinders. This burns off when you start up. If they're only slightly worn it happens when the engine cools down and a vacuum builds up in the cylinders. As they get more worn they start to leak all the time and you're oil level goes down.

 

Awesome!!