Color Splatter Brush Effect In Photoshop | How To | Random Color Spots
Select the brush tool and select the basic soft brush (hardness set to 0%)
Set up as red, green etc Set the stroke to be in normal and opacity at 100% for the stroke.
Go to the brush settings panel (window menu). Set the spacing to about 100% so you end up have some gaps in your artwork. Go to the shape dynamics and size jitter to 100% and this will increase and decrease the size as you apply the stroke. Go to the color dynamics and set the hue and saturation to 100% and this will fill the image with blurry red, green and blues etc. Set apply per tip to ON. Go to the scattering then set that to 500% so you space out both axis.
Go to the right side menu of the panel and select new. Capture size set to ON and include tool settings to ON (blending mode, color dynamics etc) and include color (in this case, red)
You can apply the stroke and fill the document with multi-colored blurry spots.
Roundness / angle
Set the roundness in the tip section to about 0% and you will see instead super thin line designs applied to your image and set the angle to 120 degrees or 90 degrees for up down strokes or zero degrees for left to right strokes. Or go to the shape dynamics and set the angle jitter to 100% have the lines changing direction across the image
If you don't won't blurry stroke, you can set the hardness (via the top left panel) to 100% to get a super sharp state.