After updating, having issues with text message app

Hi all

I have an HTC One M8.
Recently HTC sent me a text message to upgrade to Android 6, which I did.

Perhaps I shouldn't have.
Now my text messages are unreadable. Basically because the person who sends me a text, their message is in white (which is fine). My response is in black, which is...

After updating, having issues with text message app