Lyric discussion by Radioactiv 

Cover art for Plastic Rainbow lyrics by Marina and the Diamonds

To me these lyrics are a bit scattered and it's hard to find the core concept of this song.
I think what she's saying is that someone (maybe a boyfriend, an aquaintance, or possibly even her father) has turned her into a fake, cheerful girl even though she is quite negative on the inside. She's tired of being the positive one in everything, but now it's sunk in and she can't help it ("Now all I seem to do is smile"). That's all I can get from the song right now. I'll listen to it a few more times. I really like this song and all of Marina's early demos. ♥

My Interpretation