Start with a #2D2D2D background canvas, it's not necessary to use the same color but darker is easier to work with.
Create a new layer called "Skittles" and add a new layer inside the layer-set.
Set the foreground color to #980000 then with the ellipse tool, draw a semi flat circle. Dont make it a perfect circle so when we add shadows, it will have a 3D effect.