You can do this in any mode, but it's easiest on Family Fun mode. Start it up and choose no modifiers. Once in draw mode, make sure you select the Watercolor tool (if you're having difficulties finding which one it is, hover over the tools and it will show you which one it is. Watercolor is near the top left) and use it once, then correctly guess it. Once you've done this ten times, the achievement will unlock.