there is a table that says somethign like:
routine 0 purple
easy 1 purple
average 2 purple
hard 3 purple
extreme 4 purple
i believe purple dice represent the inherant difficulty of the task and black dice are random outlying modifiers or modifiers imposed by the actions of other individuals. i ran my first session last night but i think this worked. and with the issue of adding the chaos star chance, remember this, the old world is perilous and danger lurks at every turn, the shadow of chaos is constantly present in all things.