Nige is about right. Lead expands and contracts with temperature changes so paint is not really the best choice. The only thing we ever put on to lead is panitation oil which helps it weather evenly and not patchy.
There may be some kind of paint that may work that is flexible enough, I'm thinking along the lines of fabric paint that is designed to work cloth that of course doesn't stay still. I've seen tents successfully painted in this way but can't say for sure it would work with what you want.
I can't help thinking, however , why you want to do this in the first place?
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