ApiSandbox labels for optional parameters are grayed out. This is probably caused by 5c8f9d8a4ce7e4a1ba8745d3c17b4540ee006286 in OOjs UI.
The labels also don't get un-grayed when the widget's checkbox is toggled:
I haven't looked at the code in a while, but this makes me think ApiSandbox does some pretty weird things to those FieldLayouts.