Can we bring our Contigo water containers into the park?

Yes, personal water bottles are allowed. They have a nice filtered water faucet at the bathrooms designed for refilling bottles.

Last week I was there and brought Kirkland water and inspector didn't say anything at all

You can bring EMPTY bottles for water. Or any empty SIX FLAGS merchandise cup.

I have seen people bring in there water bottles that were colored. I believe as long as there is water in them you can.

Plain water yes nothing else

i don't think so... my daughter had a unopen bottle of powerade and the would not allow it to go into the park