Green white portland

I just used white portland for tile grout. It turned out with a greenish cast. The company reported other complaints.

What went wrong ?

The manufacturer that made the white portland is a big national brand. I am not going to mention the name here. I have had the same problem lately.
The best white portland cement is Lehigh, if it available in your area. Lehigh didn't pay me to say this.
We just finished a chimney here in Virginia with a brand of white portland I have never used. The color came out greenish. The homeowner came out and complained right away, and I had to paint the chimney for free.
It could have been worse. It was a natural color cement chimney on a natural color cement house. The could have insisted that I recoat the chimney. Painting was a lot less work.
There apparently is something acidic in the portland turning it green. Lehigh is always consistent. There are other brands of white portland I have used that are inconsistent. We can't use them to do addition work on houses we finished.