Market - How to remove textured background
Upload your own background
To remove the textured background, you can choose the upload your own background. You can do this under Appearance > Background and upload your own image right there.
Alternatively, if you'd like to remove the background completely and simply have a white background, you'll look for the following snippet of code in your style.css file (Appearance > Editor) and delete the line I have bolded below.
background: #fff url(images/bg.png) top center repeat-x;
font-family: 'Arimo', sans-serif;