When planted do you have to keep colors and strains
seperated to avoid cross pollination similar to Columbine?
Only for the offspring. The original plant will remain true to form/color. The reason columbine appear to change form or color is that they are rather shortlived plants and the ones that you see that have melded the attributes of specific cultivars are new seedlings, replacing the parents. Hellebores are very long lived plants and the parent plants will remain unchanged.