Bitmap-Selected
This property identifies the image to be displayed when the Check-Box control is selected. The number corresponds to the position occupied by the image in the bitmap strip. 
 
Example - Define a checkbox in screen section and define what bitmap to use when the check box is selected 
screen section. ... 03 screen-1-cb-2 Check-Box    line 27.0    column 10.0    size 116    lines 31    id 11    flat    title "My Check Box"    bitmap-handle my-cb-png    bitmap-number 1    bitmap-width 20    title-position 2    bitmap-selected 2    .  |