Help for RGB Highlights/Midtones/Shadows shader

varying mediump vec2 vTex;
uniform lowp sampler2D samplerFront;
uniform lowp float red;
uniform lowp float green;
uniform lowp float blue;

void main(void)
{
	lowp vec4 front = texture2D(samplerFront, vTex);
	
	gl_FragColor = front * vec4(red, green, blue, 1.0);
}[/code:1q7tkhkd]

To work as Highlights/Midtones/Shadows RGB correction needs 9 properties, 3 RGB for each one:

[Highlights] Modify the RGB values with 255-170 of light
Highlights RED
Highlights GREEN
Highlights BLUE

[Midtones] Modify the RGB values with 170-85 of light
Midtones RED
Midtones GREEN
Midtones BLUE

[Shadows] Modify the RGB values with 85-0 of light
Shadows RED
Shadows GREEN
Shadows BLUE

I don't know how explain, trying to find some page that explain how exactly works, but the idea is the same as the code posted but to works separated on the highlit, midtones and shadow zones of the image. So, i guess does something like that.

Any idea?