Thank you for reaching out to us about the Text-to-Join option!
The Text-to-Join feature is designed to use the texting function of the potential contact's phone so we would not be able to change the background setting of their texting application. If you are looking to change the background of the Text-to-Join printable sign this is not currently a function of this program at this time.
I do apologize for any inconvenience but I am happy to submit this as a suggestion to our engineering team to consider for future implementation.
We also have a helpful FAQ that might help with setting this up for the first time located here.
Please feel free to reach out to us if you need anything else, we're here to help!