Comment on Flowers by chronojessicapple

There are several touches you can place. Use a different colour is one, and it fades away at one point, maybe, to add variation to the background. Since your main point is the girl, you don't want too many details to distract the attention to the BG, maybe you can extend the leaves to make a curve and cut down the BG to a simple circle (something like this maybe?), and the circle doesn't have to be entirely behind the girl, she can exceed it, adding to the point she is the center of attention (like this- the character doesn't stay in the circle). You can also add shadows or lighter colours to the solid colour to show "transition" or pin-pointing light source.
I think the reason for the BG to look off is that the BG and hair goes too well together, and distracts the piece from the girl by how they seem almost to be so similar.