There’re several GUI tools for configuring the Launcher appearance in Unity 3D. But for Unity 2D, it’s kinda difficult.

This tutorial shows how to change the Launcher back-color and transparency by a little change on the code.

NOTE: YOU MUST KNOW WHAT YOU ARE GOING TO DO BEFORE

First, make a backup of /usr/share/unity-2d/launcher/Launcher.qml. Then edit this file with your favourite editor, for example:

gksu gedit /usr/share/unity-2d/launcher/Launcher.qml

Search rectangle to find out following section:

Rectangle {
Accessible.name: “background”
anchors.fill: parent
color: “black”
opacity: 0.66
visible: screen.isCompositingManagerRunning
}

Now change the color: “black” & opacity: 0.66, and it will take effect at next login.