Phil,
If you want to keep the colors of your highlights intact it is better to not tone at all or use selenium for a very short time (with the risk to loose them if you go too far) or use Sistan as Kobin said.
Now if you want to play with toning possibilities are endless.
My goal with lith printing is to get tri tones.
1) weak bleach and sepia for highlights
2) selenium for blacks
3) mid tones colors from lith.
And you can alter in many ways.
Selenium first then complete wash then bleach and sepia or polysulfide will give another complete color shif.
Gold after selenium gives beautiful colors too. It's endless
But I insist if you love the colors in the first place, especially these highlights colors... Leave them that way. I know full well how frustrating it can be when you see them vanish in the toner or after drying...
G.