You could try to boil fresh lavender in water for several hours, filter the substance and use it as a toner. I haven't tried this myself yet, so I don't know quantities, times, etc.
But is doable. Like with red onions or a lot of other plants.
For subtle colouring of selected areas, I'd suggest hand tinting with translucent paint or dye. For overall toning, a combination of iron blue and perhaps gold, maybe over the top of a lith print depending on how wild you want the colours.