Thanks indeed

Very interesting!
Let me share my findings also: if you want to set / open the colour picker with a particular colour, do:
DEFINE VARIABLE oColor AS System.Drawing.Color.
oColor = System.Drawing.Color:fromArgb(255, 0, 0). /* R, G, B values */
colorDialog1:color = oColor.
before the line:
colorDialog1:FullOpen = TRUE.
and your colour picker will open on your desired colour.