Keep the darker plume tuning and the tighter ice surface

Reverts the brighter fill: lit tops against near-black undersides, and the
higher-frequency surface undulation that separated the sheets more clearly.

6_ice_plasma.frag

@@ -63,13 +63,13 @@ void main() {
   float feather = smoothstep(0.0, 0.10, min(min(f.x, 1.0 - f.x), min(f.y, 1.0 - f.y)));
   float facet = mix(1.0, mix(0.70, 1.25, hash(cell + seed + step(1.0, f.x + f.y) * 37.0)), feather);
 
-  float shade = 0.60 + 0.55 * lit;                      // soft light across the folded planes
-  float e = mass * facet * shade * 0.075
-          + mass * (1.0 - mass) * 4.0 * 0.015           // thin torn silhouette
-          + mass * pow(lit, 14.0) * 0.045;              // glint where a fold faces the light
+  float shade = 0.05 + 1.10 * lit * lit;                // lit tops, near-black undersides
+  float e = mass * facet * shade * 0.085
+          + mass * (1.0 - mass) * 4.0 * 0.040           // thin torn silhouette
+          + mass * pow(lit, 14.0) * 0.110;              // glint where a fold faces the light
   vec3 col = e * mix(vec3(0.02, 0.42, 0.60), vec3(0.08, 0.64, 0.88), facet * 0.5);
   // Faint dye in the open gaps so darkness reads as depth, not as a hole.
-  col += smoothstep(0.40, 0.85, fbm(p * 0.30 + seed * 0.4 + o * 0.3)) * vec3(0.0001, 0.0004, 0.0006);
+  col += smoothstep(0.40, 0.85, fbm(p * 0.30 + seed * 0.4 + o * 0.3)) * vec3(0.0003, 0.0011, 0.0015);
 
   gl_FragColor = vec4(col, (0.42 + layer * 0.26) / 2.6);
 }