Just purchased a fertilizer from Gubler for the first time. Opened it up and saw that most of the fertilizer was light blueish but on the top there were some brown grains. The bag says that there is no added coloration to the fertilizer. Is the brown stuff just part of the fertilizer or did something else get in the bag?
I totally would not worry about it. They may have been packaging it from a bulk bag... a bit of bark or other stuff likely blew in. Certainly would not affect the efficacy of the fertilizer.
Pretty much all powder fertilizer formulas contain an indicator dye. Usually blue.
And when moisture invades, that blue color can go from gray to brown in color.
But I guess the thing I have to question is why you would be concerned about what’s in a container of fertilizer? Manufacturing foibles can result in appearance changes that have no bearing on the performance of the product.