Yes, you can change theme in Sense 6 (on One M7/M8) if you think that the default green background on Blinkfeed isn’t “your style” really.
In Sense 6 right now there’s 4 different themes, so far you can’t add more or do your own. We’ll see if future updates brings such features.
To change theme
You just have to go to Settings > Personalize > Themes and simply select the one you want.
You get asked if you want to change wallpaper to the one in the theme, just select No if you want to keep your current wallpaper