questions on rgb/argb

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Q1. is there a way to set an argb value to a Control?

    Private Sub Form1_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load
        Me.AllowTransparency = True
        Me.BackColor = Color.FromArgb(155, 255, 0, 0)
    End Sub

i get error when setting BackColor "control does not support tarnsparent background colors"

Q2. is there any difference between this 2:
argb(255,0,0,127) "opacity is 1, blue is half" and
argb(127,0,0,255) "opacity is half, blue is max"

Q3. what if there are rounding off errors in the conversion to/from argb/rgb
say argb(200,0,0,150) when converted to 255 opacity i get (255,0,0,117.5585938~)
can i say that argb(255,0,0,118) is exactly equal to argb(200,0,0,150) or is argb(255,0,0,117) exactly equal to argb(200,0,0,150), or is there no way to exactly convert argb(200,0,0,150) to a value with alpha at 255?

Q4. is it true that there is absolutely no relation between argb and rgb, because the actual rgb value of an argb depends on the color of the element behind it