Change the color of the Vertical thumbnails

There are two Vertical thumbnail widgets, the dark and light, but if you want to use your own colors, you can do that in this file:

WordPress

wp-content\plugins\nextend-smart-slider2-full\plugins\nextendsliderwidgetthumbnail\vertical\vertical\style.css

Joomla

plugins\nextendsliderwidgetthumbnail\vertical\vertical\style.css

For the dark thumbnail you can find the background code around line 30.:

.nextend-thumbnail-container.nextend-thumbnail-vertical-vertical1 {
width: 100%;
height: 100%;
display: block;
background: #322f2d; /* <---- */
}

The borders around line 37.:

.nextend-thumbnail-container.nextend-thumbnail-vertical-vertical1 .nextend-arrow-top,
.nextend-thumbnail-container.nextend-thumbnail-vertical-vertical1 .nextend-arrow-bottom{
width: 100%;
height: 25px;
background: url('images/vertical1-arrow.png') no-repeat center 10px;
cursor: pointer;
border-bottom: #181d20 solid 1px; <----
-webkit-transition: background-color 0.2s ease-out 0s;
-moz-transition: background-color 0.2s ease-out 0s;
-ms-transition: background-color 0.2s ease-out 0s;
-o-transition: background-color 0.2s ease-out 0s;
transition: background-color 0.2s ease-out 0s;
box-shadow: 0 1px 0px 0px rgba(255, 255, 255, 0.1) inset;
}

And around line 68.:

.nextend-thumbnail-container.nextend-thumbnail-vertical-vertical1 .nextend-thumbnail{
cursor: pointer;
overflow: hidden;
padding: 10px;
border-bottom: #181d20 solid 1px; <----
-webkit-transition: all 0.2s ease-out 0s;
-moz-transition: all 0.2s ease-out 0s;
-ms-transition: all 0.2s ease-out 0s;
-o-transition: all 0.2s ease-out 0s;
transition: all 0.2s ease-out 0s;
box-shadow: 0 1px 0px 0px rgba(255, 255, 255, 0.1) inset;
}

For the light thumbnail, the codes are the same, just look for the vertical-light instead of the vertical1. And you can change the active and hover background color in the backend.
active_hover