defining specific custom colors that will appear in the colordialog?

Question

is it possible in winforms, vb.net, to define the specific custom colors that will appear in the custom color boxes in colordialog?

Answer 1

In short, yes. MSDN covers it here. The problem is that it isn't done via Color - you need to handle the value as BGR sets - i.e. each integer is composed of the colors as 00BBGGRR, so you left-shift blue by 16, green by 8, and use red "as is".

My VB sucks, but in C#, to add purple:

    using (ColorDialog dlg = new ColorDialog())
    {
        Color purple = Color.Purple;
        int i = (purple.B << 16) | (purple.G << 8) | purple.R;
        dlg.CustomColors = new[] { i };
        dlg.ShowDialog();
    }

reflector assures me that this is similar to:

Using dlg As ColorDialog = New ColorDialog
    Dim purple As Color = Color.Purple
    Dim i As Integer = (((purple.B << &H10) Or (purple.G << 8)) Or purple.R)
    dlg.CustomColors = New Integer() { i }
    dlg.ShowDialog
End Using

Answer 2

The existing example contains an error.

purple.B is a byte not an integer, so shifting it 8 or 16 bits will do nothing to the value. Each byte first has to be cast to an integer before shifting it. Something like this (VB.NET):

Dim CurrentColor As Color = Color.Purple
Using dlg As ColorDialog = New ColorDialog
    Dim colourBlue As Integer = CurrentColor.B
    Dim colourGreen As Integer = CurrentColor.G
    Dim colourRed As Integer = CurrentColor.R
    Dim newCustomColour as Integer = colourBlue << 16 Or colourGreen << 8 Or colourRed
    dlg.CustomColors = New Integer() { newCustomColour }
    dlg.ShowDialog
End Using