Still not entirely sure what you're aim is but

maybe you could convert rgb to hsv, adjust then convert back to rgb again

```
uniform vec4 color : hint_color = vec4(1);
uniform float Hue : hint_range(0.0, 1.0, 0.1) = 1;
uniform float Saturation : hint_range(0.0, 1.0, 0.1) = 1;
uniform float Value : hint_range(0.0, 1.0, 0.1) = 1;
vec3 rgb_to_hsv(vec3 c)
{
vec4 K = vec4(0.0, -1.0 / 3.0, 2.0 / 3.0, -1.0);
vec4 p = mix(vec4(c.bg, K.wz), vec4(c.gb, K.xy), step(c.b, c.g));
vec4 q = mix(vec4(p.xyw, c.r), vec4(c.r, p.yzx), step(p.x, c.r));
float d = q.x - min(q.w, q.y);
float e = 1.0e-10;
return vec3(abs(q.z + (q.w - q.y) / (6.0 * d + e)), d / (q.x + e), q.x);
}
vec3 hsv_to_rgb(vec3 c)
{
vec4 K = vec4(1.0, 2.0 / 3.0, 1.0 / 3.0, 3.0);
vec3 p = abs(fract(c.xxx + K.xyz) * 6.0 - K.www);
return c.z * mix(K.xxx, clamp(p - K.xxx, 0.0, 1.0), c.y);
}
void fragment(){
vec3 hsv = rgb_to_hsv(color.rgb);
hsv.x *= Hue;
hsv.g *= Saturation;
hsv.z *= Value;
# for 2d
COLOR = vec4(hsv_to_rgb(hsv), color.a);
# for 3d
ALBEDO = hsv_to_rgb(hsv);
ALPHA = color.a;
}
```

You can adjust both the SV values to as you called it **"desaturate"**