How to change the background in embedded Webmixes
Step 1: Start by sharing your Webmix (if you've done this, skip to Step 3)
Step 2: you will be prompted with the Webmix share options. Please click on the "Embed" button
Step 3: You will then see the embed code for your Webmix; Click the "Set Background" button, and you will then see multiple colors that you can choose from; and lastly you have to select the updated code once you are done selecting the background's color.
To learn how to Re-Publish/Re-Share your Webmix, please click here.