I tone MGIV RC pearl paper for 3 min @ 1:9 dilution. There is a slight shift towards blue/purple, but I find it nice, better than an un-toned print, and the blacks are certainly deepened. Your paper developer will also slightly affect the color shift as well, although I don't believe as much with RC as with FB and not nearly as much as with warmtone papers.

I'd recommend trying the 1:9 dilution for 2-3 minutes and see with you think. You'll still get a slight color shift, but your blacks should be deeper. Good luck!