The color of the screen (background).
This property can be set to any named color value (e.g., white, blue, green, lightyellow, ...).
The following block randomly sets its background color to yellow or white:
<block someblock>
/ trials = [1-10=test]
/ ontrialbegin = [if(rand(1, 100) > 50) { block.someblock.screencolor = yellow; } else { block.someblock.screencolor = white; } ]
</block>