When I have a page with several visualization, usually from related data, most of us use the same color by for the same variable in all visualization.
It looks a little weird to add it only on the first one and tell the customer to assume the same color to the others visualization.
At the same time, it´s redundant to have it on all viz. so it will be usefull to have some mane with the legend that will also look like it really apply to all graph.