Drop down Menu background color, Mobile

Hi Nadia, for this kind of problems it’s better to use some tools to figure out what to change in your custom css. Tools like Firebug, or Chrome’s/Safari’s developer tools.
Said that, the drop down menu is “ruled” by these line, for example, in the blue.css:

@media (max-width: 979px)
.nav-collapse, .nav-collapse.collapse {
overflow: hidden;
height: 0;
position: absolute;
z-index: 3000;
right: 0px;
top: 42px;
background-color: #fafafa;
background-image: -moz-linear-gradient(top, white, #f2f2f2);
background-image: -webkit-gradient(linear, 0 0, 0 100%, from(white), to(#f2f2f2));
background-image: -webkit-linear-gradient(top, white, #f2f2f2);
background-image: -o-linear-gradient(top, white, #f2f2f2);
background-image: linear-gradient(to bottom, white, #f2f2f2);
background-repeat: repeat-x;
filter: progid:DXImageTransform.Microsoft.gradient(startColorstr='#ffffffff', endColorstr='#fff2f2f2', GradientType=0);
-webkit-border-radius: 4px;
-moz-border-radius: 4px;
border-radius: 4px;
-webkit-box-shadow: 0 2px 10px rgba(0, 0, 0, 0.25);
-moz-box-shadow: 0 2px 10px rgba(0, 0, 0, 0.25);
box-shadow: 0 2px 10px rgba(0, 0, 0, 0.25);
}

So you should put in your custom css, or in your child theme style.css this:

@media (max-width: 979px)
.nav-collapse, .nav-collapse.collapse {
background-color: YOURCOLOR;
background-image: -moz-linear-gradient(top, START_COLOR, END_COLOR);
background-image: -webkit-gradient(linear, 0 0, 0 100%, from(START_COLOR), to(END_COLOR));
background-image: -webkit-linear-gradient(top, START_COLOR, END_COLOR);
background-image: -o-linear-gradient(top, START_COLOR, END_COLOR);
background-image: linear-gradient(to bottom, START_COLOR, END_COLOR);
background-repeat: repeat-x;
filter: progid:DXImageTransform.Microsoft.gradient(startColorstr='START_COLOR', endColorstr='END_COLOR', GradientType=0);
-webkit-border-radius: YOUR_NEW_BORDER_RADIUS_IN_px;
-moz-border-radius: YOUR_NEW_BORDER_RADIUS_IN_px;
border-radius: YOUR_NEW_BORDER_RADIUS_IN_px;
}

so replace those YOURCOLOR, START_COLOR, END_COLOR, with the colors you choose (http://www.w3schools.com/cssref/css_colors.asp).
About YOUR_NEW_BORDER_RADIUS_IN_px, for example if you don’t want round borders at all then replace those YOUR_NEW_BORDER_RADIUS_IN_px with 0px.