How exactly Windows 10 detects if it should use a black or white title?

With the latest stable build of Windows 10 (10586), the color of the title of Win32 windows changes respecting the color of the window chrome.

For example, if the window color is darker, the title uses a white color. Vice-versa.

So, since I want that that kind of behavior, I had to get the brightness of the color of the window chrome.

By using this method:

public static int GetBrightness(this Color c)
{
    return (int)Math.Sqrt(
    c.R * c.R * .241 +
    c.G * c.G * .691 +
    c.B * c.B * .068);
}

And I was using this other method:

public static float GetBrightness2(this Color color)
{
    float num = ((float)color.R) / 255f;
    float num2 = ((float)color.G) / 255f;
    float num3 = ((float)color.B) / 255f;
    float num4 = num;
    float num5 = num;
    if (num2 > num4)
        num4 = num2;
    if (num3 > num4)
        num4 = num3;
    if (num2 < num5)
        num5 = num2;
    if (num3 < num5)
        num5 = num3;
    return ((num4 + num5) / 2f);
}

So all I had to do was test all of the colors to get a threshold (First method, second method):

White Title: 
127 0,58
120 0,55
105 0,39
127 0,34
101 0,43
109 0,43
105 0,44
86 0,31
105 0,36
83 0,32
68 0,26
136 0,47
106 0,41
108 0,44
109 0,42
110 0,39
89 0,34
108 0,58
105 0,25
83 0,34
75 0,29
108 0,39
106 0,40
108 0,51

Black Title:
189 0,47
161 0,47
138 0,65
150 0,35
143 0,32
138 0,58
161 0,37
167 0,45

Only a few bunch of colors resulted in a black title color and the threshold apparently is 137.

The problem happened when I selected the Automatically pick an accent color from my background:

Automatic, Black Title:
132 0,37 Color: {#FF94842D}

As you can see, 132 is smaller than 137, yet it shows a black title. So my GetBrightness() method may differ from the one that Windows uses.

So, how exactly Windows 10 decides what color the title should use?

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