Hi,
Rather than provide a parameter for an explicit background colour we instead add the data-chrome=“transparent” option; this allows you to set a background colour, image, or CSS gradient on the container and have it show through, rather than needing to provide every permutation to the widget. So, add that and you should be able to get what you want there.
As for removing user avatars: User identity and attribution is something we regard as really very important, and as such, our Tweet layout and anatomy regards the name and icon for a user as essential. Therefore, we’re not considering adding that option to our timeline tool at this time.
Now, I hear the argument that it may be repetitive when displaying a single user’s timeline, but in that situation it’s especially important to us that Retweets are well attributed in amongst the others; that’s how we do it on the website, too.
Ben