She dips the paint brush and playfully flings it against the white walls revealing the lyrics in layers of bold color - seemingly magically. She could also paint bold strips with a roller-brush or even spray-paint to reveal the lyrics on the walls.
During a performance setup, thick waterfalls of color could seem to run down from the wall to reveal the lyrics and bathe the white room in new, bold shades.
The trick is to shoot this on a green screen set — with limited "real" paint - and perhaps none at all. All of the magic would happen in post utilizing various paint drip and splatter collections for After Effects to reveal the words on screen.
The brush / brushes and paint cans would be blue allowing us to dial in any color for the paint itself while keeping the background white (or any color we want).
Lindsay could remain as clean, or get dirty as she wants to be in a virtual paint environment.
Another interesting aspect of doing the lyric video with this technique is that she could appear to paint the air, or give the appearance that she is painting glass.