Hi CE_Chgo,
Multigrade IV FB responds subtly to selenium; the original warm-ish image cools tone off to very subtle blue. That's why it's difficult to split-tone if you use selenium first - it's almost impossible to find the 'snatch-point'.
I've used the Fotospeed selenium product; how that varies from the Kodak, or other similar products, I don't know. I've *never* acheived purple-ish tones with Multigrade IV papers in selenium. Give it about ten minutes, checking it against a similar untoned print in a dish of water.
Another paper I found reacted similarly was Kentmere Fineprint VC, although there's no discernible change in selenium IIRC.