That's an interesting piece that plays with depth perception. I like that the colors don't change even when they should be. For instance, the portions of the chair behind the glass table are the same as the portions of the chair in front of the glass table. For that effect, you might have to play with z-buffering while breaking apart portions of the model you want to have that effect.

To get that very flat look I think you'll have to use an emission texture that emits right at the camera regardless of the angle.

The other interesting thing are the shadows. The artist seems wants to be very selective about where they wanted to have depth. The tree leaves cast shadows but the pots and tree trunk don't seem to receive any shadows. The furniture cast shadows, but not everything. The stairs, for example, do not cast shadows. If you look closely, the artist is using texture to emulate shadow. It's going to be a mix of lit and unlit shaders with shadow planes for select objects.

Overall, fascinating style to try to emulate in Blender.