Here is the simple info on the color means when you use poly filter.
It turns blue with a copper salt, light green to aqua with free copper, orange with iron, red with aluminum, yellowish green with ammonia and white to beige to brown to black with the absorption of harmful organics.
Here is an FAQ.
http://www.poly-bio-marine.com/faq.htm
Disclaimer : I got zero profit from this product. Just sharing as a user like HM.