Hi @RAppleton ,
I checked the HTML on these custom email templates, and I was unable to change the color of the Join button. I am no HTML expert, but it seems the button itself has its own set of characteristics that cannot be edited and is considered %iCalendarSection%.
I was going to suggest a workaround, which would be to upload a picture of your own Join button that you create with your own branding and hyperlink it with the join link, but it seems you have to use a link address for whatever image you want to upload and hyperlinking only applies to text rather than images.
In this case, I was able to DELETE the %iCalendarSection% and replace it with the HTML as below:
<div style="text-align:left;"><a href="https://cisco.webex.com/cisco/j.php?RGID=rec00988ae640ef6a931b69bf543eface"><img src="https://community.cisco.com/t5/image/serverpage/image-id/153078i615461A9FA8AB1D5/image-dimensions/300x100?v=v2" /></a></div><br />
The bold part of the HTML above should include the link to join the meeting. The not bold part of the HTML should include the link to the image you want as the join button.
