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 ureadable as I have a dark background for SMS.

I have tried but cannot either
1. Change the background to a more friendly color or
2. Change the color of the font.

HELP! Please. It's driving me crazy.

ANY help appreciated