This is a format preference in the Trade Mode Preference Panel under Appearance that controls the degree of lightness or darkness of a color of an object. In particular, this is used to display held Buy or Sell orders (Time Release, bracket, OCO, etc.) on the chart in the Order Entry Toolbars. Compare the two Figures below.
To change the opacity of a held order, enter a numeric value in the row.
This affects the Order Entry Toolbar.