@XivitTW It's a spray brush with kinda like this texture. I'll make sure and make a tutorial for this sort of brush and its uses.
Main idea is to apply the color then invert it to "eraser" mode and touch it up.
"Caustics" in 146 chars of #GLSL
vec2 p=FC.xy/r.y*2e1+t;for(float i;i++<8.;)p+=sin(p+t/.2+i)*.4,p*=mat2(6,-8,8,6)/9.;o=vec4(tanh(length(fwidth(sin(p*.3)/.1))),texture(b,FC.xy/r));
