vec3 col;
if (isColorMode) {
    col = (d > 0.0) ? externalColor : internalColor;
    col *= 1.05 - exp(-6.0 * abs(d));
    col *= 0.8 + 0.2 * cos(110.0 * d);
    col = mix(col, vec3(1.0), 1.0 - smoothstep(0.0, 0.01, abs(d)));
} else {
    col = (d > 0.0) ? vec3(1.0) : vec3(0.0);
}