I'm starting with background color as a test, since it takes html I thought this would change the balloon BG color but it's not working.
<html> <body bgcolor="#E6E6FA"> <img src="https://seamlessrnc.nauticalcharts.noaa.gov/rnc/noaa_ocs_small_banner.jpg"></a> <BalloonBGColor = '-1' BalloonFGColor = '-16777216' BalloonBGColorField = ''red" > </body> </html>