they took away the freedom and customization ability to change the text message background and chat bubbles away once and veiled their Galaxy store so they could force you into buying their junk. With the update today you can finally change the background but still no chat bubble. I don't want a thyme to change everything just so I can change the chat bubbles only, that is absolutely ridiculous
although the ability to change the messages text bubbles isn't built in, there are 3rd party apps you can use to get the exact things you're looking for. Textra is a 3rd party messaging app that doesn't require your contacts to use it for you to send them messages. There are so many customization options for it and it's been around forever, very reliable and has high reviews on the Google play store.
You can also change your phone's theme, a lot of theme developers change the messaging background and text bubble colors with their themes.
I know you want the option to just be built into the default app, but since it's not, these are some options for you. Hope this helps.
