Use the mouse to select your sand color and drop it to make patterns. Space bar also works for both selection and dropping. Drag the color picker to where you want. C key hides or shows the color picker. Works best in full screen mode because the color picker is pretty small. Enjoy!
I took a screen capture of the Scratch color palette for the color picker. The color on the top row to the far right (where transparent usually is) is a random color pick - it puts out sand grains of all colors :)
