Oh, ok, I gotcha. I would say you should color that in now... but make it way more round by shading in around it... if it's a 3/4 moon it's not reading well. If you do light grey-blues and do the texture of the moon, i think it would be kick ass.
I have been checking this one out for the past couple days and the only thing that bugs me is that roundish shape in the background made up of the shading... Not sure what it is but my eye is drawn to it distracting from the whole piece. Tangents are a bad