I'm unaware of anyone who says 'work in the black' or 'work on the black'.
I think the set phrase in Spanish means to work illegally (or at a job that isn't official), but it could be something else.
If the 'illegal' component isn't inferred, we say:
take a job on the side
burn the midnight oil
work for pocket change
have a second/night job
moonlight
supplement one's income (on the side, on the down low)
Last edited by Rusty; March 06, 2018 at 04:14 PM.
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