The first image attached is an example of the color I get with Ferric Oxalate developer at 60C. The paper is Arches Aquarelle HP. On Arches Platine I usually get more neutral tone.
I have also used Sodium Acetate developper but it gives me quite neutral tone (the image with the roses).
Sodium citrate developper gives quite interesting color but it producess a lot of bronzing for me that I could not control (the third image).