Trendy or not painting plants is a surefire way to kill them. Plants have pores (stomatal pore) that are located mostly on the surface of leaves. These pores are how plants gain access to carbon dioxide to carry out the process of photosynthesis. They are tiny and typically not visible with the use of a microscope.
When we paint the surface of the plant we block the ability for the plant to exchange gasses with the atmosphere. When this happens the plant is no longer able to gain access to convert carbon dioxide into sugars.
Something else happens when we paint plants is the blocking of sunlight. Plants unlike animals make their own food. Now some marketing campaigns have lead us to believe that by adding fertilizers to water we are feeding plants. Which is a flat out lie. Plants make their own food through the process of photosynthesis. But in order for this pathway to happen plants need access to light.
Instead of painting plants for the holidays consider painting the pots. It is a fun interactive and safe for the plants.