Is money earned from working in the field of repacking old paints into new containers, which are then sold as new, considered lawful (halal) or unlawful (haram)?

What you earned from your work is permissible (halal) as long as you were not his partner and you knew about it. There is no sin upon you for what you did, due to your lack of knowledge of his malicious intent; for Allah the Almighty says: "And there is no blame upon you for that in which you err, but [there is blame for] what your hearts intended."