IM new using POR-15 and heard it will turn a light gray on you if exposed to light so would that apply to the chassis since it underneath the car. Im going to use it on my chassis and wanted to know if im doing the chassis and control arms would i need to use a over coat on them also or not thanks.

Not to be snarky, but a good source to answer your question would be http://www.por-15.com/
There's a lovely FAQ (http://www.por15.com/faq.asp) that says:
MUST I PAINT OVER POR-15 TO MAKE IT LAST?
No, but POR-15 has an ultra-violet sensitivity and must be topcoated if continually exposed to sunlight. Once topcoated, POR-15 will remain effective for many years.

WILL THE SUN DESTROY MY POR-15 COATING IF I DON'T TOPCOAT IT?
No, your POR-15 protection will remain, but the sun will change its appearance cosmetically. That's why we recommend you topcoat it.
All kinds of other info and products on the web site.