Drawing a color wheel with fxc shader in a WPF app

I want to achieve something like this with fxc shader in a WPF application.

So far, with the below hlsl (High-Level Shading Language) code, I managed to produced this picture:

The problem is that I cannot find a way to:

1. Move green corner (left, bottom) to left, top.

2. Move blue corner (left, top) to right, top.

3. Right, bottom corner should be red and left, bottom corner - gray

4. Also the wheel itself doesn't look the same.

The hlsl code:

// ColorWheelEffect.hlsl
#define PI 3.141592653f
#define value 1.0f

float4 main(float2 uv : TEXCOORD) : COLOR {
    uv = 2 * uv - 1;
    float saturation = length(uv);
    float hue = 3 * (PI - atan2(uv.y, -uv.x)) / PI;
    float chroma = value * saturation;
    float second = chroma * (1 - abs(hue % 2.0 - 1));
    float m = value - chroma;
    float3 rgb;
    if (hue < 1)
        rgb = float3(chroma, second, 0);
    else if (hue < 2)
        rgb = float3(second, chroma, 0);
    else if (hue < 3)
        rgb = float3(0, chroma, second);
    else if (hue < 4)
        rgb = float3(0, second, chroma);
    else if (hue < 5)
        rgb = float3(second, 0, chroma);
    else
        rgb = float3(chroma, 0, second);
    return float4(rgb + m, saturation < 1);
}