How can I change the background color of text messages on the Sony Xperia Z Ultra?

First

The background color when I send text messages is its default color of blue (the text being white), but I want to change the background color from blue. How can I do that? Thanks in advance.

BM08

It may help people answer if you told us what app you use to text? Is it the built in one or is it something like WhatsApp?

First

It's the app that comes built in with the phone. I never downloaded any text messaging apps onto the phone.

I attached a picture of what I'm referring to. I hope the quality isn't too bad...

BM08

What phone is it? Should be something in the setting menu to adjust it