Water based use water based, universal or alcohol aniline dyes. Oil based, epoxy compatible, alcohol or oil based. However, a bit of caution - you need to test how it reacts and how it actually looks. Stacking/layering tints can get tricky.
I just did it on a recent table build the original color was an light amber with blue effervescence highlight. But, the blue actually neutralized the amber to a almost clear. So, I had to re-shoot the top with a dark amber to counter act and then I got the look /tint shade I wanted.
It worked out but my lesson was humble pie ... best laid plans of mice & me ......
Tinting finishes it not my thing but it seems like you should be able to mix say common Watco Danish oil in a dark, medium or light walnut color and get a darker tint.
Oil on oil. Water on water. With polyurethane just add stains to get the color you want. That's all polyshades is.
Add a little at a time. Trans tint dye works as well. Be careful with Trans tint. A little goes a long way.