First off, the background is not grey. It’s kind of a watercolored effect of grey, blue and green that comes off as a muted greyish tone in most places. But it definitely isn’t just grey. And I will fight anyone that says it is.
Secondly, it doesn’t matter what the forms are meant to be. What matters is that they are meant to be both positive and negative within the space. They are meant to both work as sharpness and softness against the background, and that is why the background tone is watercolor muted and mixed as it is – to give the distinct definition that the angles and fluid lines need in order to work as they need. And I will fight you if you say otherwise.