Ilford Warmtone fibre (glossy) is my favourite paper. I always selenium tone it, to enrich the print's appearance, using Harman selenium toner at 1+3. As you have discovered this does darken the shadows. Two ways you can deal with this are:

1. Selenium tone as part of of the process, not as an add-on afterwards. When my print comes out of the fixer I wash it for 1 minute, then soak it in hypo clear for 1 min. then selenium tone it. If the shadows go too dark I can then easily do another print. I sometimes do this with test strips too.

2. Aim to first get an untoned print that looks good in the shadows and highlights when judged wet. For the final print knock 10% off the exposure time. This will take care of dry down in the highlights. The shadows will also look lighter but will darken down to what they were (or a little darker) when you selenium tone the print.

I watch the print like a hawk when it is in the selenium toner, and transfer it to water as soon as I see a colour change -or indeed any change- start to occur. I like prints with just a hint of colour change.
As far as the colour is concerned I find that if I develop in Neutol WA I get a coolish brown/purple, and if I develop in Harman Warmtone I get a warmer colour. I prefer the latter, but others may not.

When you get used to this paper and how it changes in selenium you will find that you won't need to do step 2 so rigorously. The whole process will become intuitive and easy to control.
Hope this helps.

Alan Clark