iron gallate and iron tannate pigments are very lightfast and permanent. The trick with making excellent neutral tone cyanotypes lies in controlling their color and keeping the pigments put in place. Both can be solved. Much of the process is sensitive to oxidation of the toner and so you can get very variable results in a darkroom setting. Waiting five minutes before toning vs. waiting 20 minutes will give different results. Also, the time spent in the toner affects this. Tricky tricky.