Paint is another way for poker players to refer to face cards, such as jacks, queens, and kings. Since face cards have intricate designs and a lot of colours, the players have coined the term paint to refer to these playing cards that have the most printing ink on them.
However, one thing to note is that poker players often play other casino games as well. More importantly, the terminology picks up and spreads somewhat fast when there are a lot of people using the same term. Therefore, you shouldn’t be surprised if you hear someone using the term paint to refer to face cards even if they are playing a game other than poker.