Begin by opening your web backdrop file in Photoshop. Fill your backdrop to a solid black (Shift+F5). Select the Gradient tool, 50% Opacity and set a warm Foreground colour (#ff7521). Apply to the top of your backdrop using a colour to transparent Linear style Gradient. This will work as your base tone.
Select your brush set to 0% Hardness, increasing to a large size. Set both Opacity and Fill at 50%. Apply varying tones over your gradient colour. Next, create a new layer and select a brush type that scatters well, we’ve selected the Grass brush style. Apply this with varying brush sizes, using a colour picked from your backdrop, with Opacity and Fill both reset to 100%.
Finally, with your new painted layer active, select Filter>Pixelate>Mosaic, setting Cell Size to 25 square. Also apply Filter>Noise>Add Noise, setting an Amount of 1%. If you want to alternate your pixel tones you can simply adjust using colour adjustments, ie Hue/Saturation, or even experiment with layer blending modes.