Some forms of epileptic seizure can be triggered by lights (such as
portions of computer screens) flashing at certain frequencies. As
such, US federal and most state governments prohibit use of flashing
text in government computer applications (which would include
documents using flashing text). In the private world, if your
spreadsheet were to trigger someone else's seizure, you or your
employer could be sued, and the plaintiff's chance of winning such a
suit may be pretty good.
