Noise

Three octaves of value noise (each half the amplitude, twice the frequency, drifting in a different direction) summed into one continuous field, then colored the same way plasma is — iAccent plus three fixed hues.

Value noise is a smoothed hash grid: pick a random value at every integer lattice point, then bilinearly interpolate between them with a Hermite-eased fractional. Stacking octaves adds detail without breaking the smoothness — the classic recipe for organic-looking texture.

[glsl]: shader source

// Three-octave value-noise field cycled through a four-color palette.
// @slider tempo 0.1 3.0 1.0 0.05
uniform float tempo;

float hash(vec2 p){
  return fract(sin(dot(p, vec2(127.1, 311.7))) * 43758.5453);
}

// bilinearly-interpolated hash grid, Hermite-smoothed
float valueNoise(vec2 p){
  vec2 i = floor(p);
  vec2 f = fract(p);
  f = f * f * (3.0 - 2.0 * f);
  return mix(
    mix(hash(i),                  hash(i + vec2(1.0, 0.0)), f.x),
    mix(hash(i + vec2(0.0, 1.0)), hash(i + vec2(1.0, 1.0)), f.x),
    f.y);
}

void mainImage( out vec4 fragColor, in vec2 fragCoord )
{
  vec2 uv = fragCoord / iResolution.xy;
  float t = iTime * 0.2 * tempo;

  // three octaves: each half amplitude, twice frequency, drifting different way
  float n = valueNoise(uv *  5.0 + t)         * 0.5;
  n     += valueNoise(uv * 10.0 - t * 0.5)    * 0.25;
  n     += valueNoise(uv * 20.0 + t * 0.3)    * 0.125;

  vec3 c1 = iAccent;
  vec3 c2 = vec3(0.35, 0.75, 1.00);
  vec3 c3 = vec3(1.00, 0.35, 0.55);
  vec3 c4 = vec3(0.55, 0.25, 0.85);
  float idx = n * 4.0;
  vec3 col;
  if(idx < 1.0)      col = mix(c1, c2, idx);
  else if(idx < 2.0) col = mix(c2, c3, idx - 1.0);
  else if(idx < 3.0) col = mix(c3, c4, idx - 2.0);
  else               col = mix(c4, c1, idx - 3.0);

  fragColor = vec4(col * 0.4, 1.0);
}