There might be a problem with your naming.
I made a standard Windows Forms project, with 2 buttons and added some code, when clicking the buttons their respective colors do actually fade away.
And I agree with Jon Skeet, you are implementing a duplicate method, also all parameter names should begin with a lower case letter, so 'a' instead of 'A'
code:
private void Form1_Load(object sender, EventArgs e)
{
button1.BackColor = Color.Red;
button2.BackColor = Color.Green;
}
private void button1_Click(object sender, EventArgs e)
{
Color c = button1.BackColor;
button1.BackColor = Color.FromArgb(Math.Max(c.A - 10, (byte)0), c.R, c.G, c.B);
}
private void button2_Click(object sender, EventArgs e)
{
Color c = button2.BackColor;
button2.BackColor = Color.FromArgb(Math.Max(c.A - 10, (byte)0), c.R, c.G, c.B);
}
public static Color SetTransparency(int a, Color color)
{
return Color.FromArgb(a, color.R, color.G, color.B);
}