My frustrating marble painting!

Well, I was excited, at first about this painting, but am quite peeved at myself now that it's finished. I wasn't paying attention to the pencil I used to draw my grid and accidentally used my grey watercolor pencil. Now, you might think that was a good thing because the color would wash away, but no, that pencil loves to grab the paper and never erases off. I did my best to wash it, over and over, but to no avail. I was hoping the paint would cover it, but no, it's still visible and it's the pits! I used a photo by a member of WetCanvas, Mustcreate, and I thank them for allowing me to use it. I have had some suggestions of how to fix it such as adding checks to the background or tiles, but I'm too mad to mess with it now, maybe tomorrow. The marbles are swell, just not the background. I guess we all live and learn!