Some people have noticed that when Cooper returns to the "purple room" in part 3 and meets the American Girl, there is also a blue rose on a table, probably a formica table. It is hard to notice it when watching a compressed video stream.
But something else caught my attention, it is the contrast between these two scenes:
Cooper's first visit has the room lit in an ambient reddish hue (the transition from purple to red is very noticeable here), but the second visit loses the reddish glow. If you look at the ceiling, the texture is that of the lunar surface. Two additional lamps are shown rather dimly, and each casts a shadow that resembles a lunar eclipse. This scene loses the ambient lighting, and the only natural source seems to be that of the ceiling (or the Moon).
What to make of it? I do not know, except that the first scene may have something to do with Mars ("Mars door"), and the second with Moon ("Moon door"), whatever that may mean (may be be related to different chakras).