I made some prints yesterday on the same paper as you used and developed them in Neutol WA at a dilution of 1+9. They have no hint whatsoever of any colour cast;just a nice neutral grey. Before complicating things by adding things to your developer, or using selenium toning, why don't you just change developer?
Actually Ilford Multigrade is quite bullet-proof in its resistance to colour change from different developers so you won't get a warm tone out of it by using a warm-tone developer. I use NeutolWA (warm tone) because I also use it on warm tone papers, so standardise on it. It does a lovely job on Multigrade, and after using it, if not exhausted can be bottled and re-used later because at working strength it keeps very well. Handy for short sessions.