Make a copy of your stylesheet before you make these changes
find this in /wp-content/themes/{themename}/style.css (line 82)
table {
border-bottom:1px solid #E0DED9;
border-collapse:collapse;
border-top:1px solid #E0DED9;
margin:15px 0;
width:100%;
}
delete
border-bottom:1px solid #E0DED9;
border-top:1px solid #E0DED9;
add
border: none;
find this (line 90)
td {
background:#F5F3EE none repeat scroll 0 0;
border-bottom:1px solid #FFFFFF;
padding:4px 6px;
}
change
border-bottom:1px solid #FFFFFF;
to
border: none;
What you are calling beige background looks grey here. Anyway, that is coming from several places in your stylesheet. The color code is #F5F3EE. Anywhere in the stylesheet that is the background: or background-color: replace it with the color code you prefer.