WinStudio
This attribute determines the amount of transparency for the specified extended color. The range is 0 to 255, with 0 being totally transparent and 255 being totally opaque.
The Ext. Color Alpha 0 setting affects only Ext. Color 0, and Ext. Color Alpha 1 affects only Ext. Color 1.
About Setting Form and Component Background Colors
Ext. Color - Gradient Direction Attribute