This will change the color to white. Locate .site-header
in your css (should be around line 1159)
.site-header {
background-color: #000;
border-bottom: 1px solid #ddd;
left: 0;
position: fixed;
top: 0;
width: 100%;
z-index: 999;
}
Change #000
to #fff
.site-header {
background-color: #fff;
To add space to the left of the logo. Add margin-left: 20px;
to .site-title a
.site-title a {
margin-left: 20px;
}