Hey Gordon -
If it's any consolation (it probably isn't), employees of Tableau get to see this, too. Even as a semi-admin on the site there is no way I can get screaming big orange to go away. I think it's hard coded.
There's another really long thread elsewhere in this forum where people are talking about it - you might want to "pile on" in there.
It's not even a css element, so I can't even use a custom css
If you really wanted to make a project of it, you can probably use a browser add-in like this one to block specific images:
Let me know how it goes if you try - I might follow suit