Forground picture shows confetti effect.
Made brush from only 3 shapes filled with black, as indicated within the red circle.
Set the brush prameters for high scattering, size variation, and color variation.
By setting the forground and background colors far apart, result is wide variety of colors.
In the back image, I applied brush to three different layers
with brush size change on each, trying to simulate depth.
Applied layer styles: bevel/emboss and glow
Finally, blurred the largest ("closest") layer.