Since I love customizing the theme and would love you to customize the Photo-Biyori, I’ll show you here how to customize the background color of the Photo-Biyori site. It’s pretty easy. ;)

First, here is the sample.
This is the default color for the PB LT and this is after.

Changes:
in style.css:
background-color: #xxxxxx; inside body, #wrap, #header and #footer tags.

in header.php:
background-color: #xxxxxx; inside <style type="text/css" media="screen"></style> tag.

In the sample site, I changed it to #000000 (black).

Depend on the color you pick, the title text might not look good. In that case, change:

style.css:
#xxxxxx after /* blog title text color */