Webhook from AWS Lambda Color Side bar

I have a backup job running within AWS. I have an AWS Lambda function running where it then has a webhook into MatterMost where it posts the results into a specific channel. This is all working perfectly. However now I am wanting to see if I could customize this message. Is there a way to add a color to the message (Left side), similar to the system messages? I am using python within Lambda.

Thank you in advance.