It would be a hack, but you could create a background image of the colored grid like I did here: http://dataremixed.com/2011/11/how-to-win-at-monopoly/.
How to do it:
1. Create the grid with your spreadsheet or graphics tool of choice and save as a jpeg or png,
2. upload your image to your scatter plot using Map > Background Images > Add Image...
3. You'd then have to size the image to match your x (0-100%) and y (0-6000) axes.
The only problem with this approach is you'd really need to fix both axes, so if the data values ever changed such that any of them went went beyond the max, those data points would not be shown.
Hope this helps!
Thanks Ben. It should help.