Sketchpad in coroutine not honoring background color settings

[dschreij]

See https://forum.cogsci.nl/discussion/6598/osweb-collecting-keyboard-response-while-presenting-multiple-sketchpads
for a discussion.

A sketchpad that is inside a coroutine always has a black background. It ignores the global background setting of the experiment, and setting a background color explicitly with for instance set background orange in the sketchpad script also does nothing. The (global) foreground color is processed though.