A slight variation on Kodak T-12 Iron Blue Toner, with some usage notes for acheiving bright, saturated cyanotype tones. It's easy to mix up on the spot. In fact, I don't think it will keep once the ferricyanide has been mixed in, so this is a one-shot.

500 ml water
1/2 teaspoon ferric ammonium oxalate (ferric ammonium citrate works too)
1/2 teaspoon sodium bisulfate (or some other acid - oxalic, tartaric and citric probably work too)
1/4 teaspoon potassium ferricyanide

Bathe prints for a few minutes, then wash and transfer to a bath of neutral or acidic fix. Most of the blue tone will disappear, as will the yellow paper stain. After about a minute, wash the print again, and put it back in the toner. The blue will come back stronger this time. Transfer to a weak alkali bath to clear out the yellow stain:

500 ml water
1/2 teaspoon borax (another weak base will likely work too)

Don't leave the print in the clearing bath - it will likely start bleaching out the blue. Finish up with a wash.

I've tried this with a variety of RC papers: Ilford Multigrade Warmtone, Agfa MCP and Kentmere VC Select.