What color hair dye last the longest?

Well, it all depends on how well you take care of it, personally I think pravana or splat. Pravan because it is a salon quality dye and as it fades it turns different colors of the dye (for example royal blue, navy blue etc) and Splat because I had blue hair and I didn't have to re dye until my roots grew back like really bad, Manic Panic is the healthiest one but it fades really fast and so does ion. Hopes this helps!