There are two options for screenshots.
The first being that you would have to edit the Kobo eReader.conf file located in the Kobo directory inside the .Kobo directory. Under the [FeatureSettings] header, you would add a line reading 'Screenshots=true' (case sensitive) which then allows you to take a screenshot by pressing the power button. Note that this makes the power button useless for waking your Kobo up.
Code:
[FeatureSettings]
Screenshots=true
The other option is to install NickelMenu. You can download the KoboRoot.tgz installer from the download link in the first message in the
[color=blue]NickelMenu: An integrated launcher for Kobo eReaders[/color] thread. Once you have the KoboRoot.tgz file, copy it to the .kobo directory on your Libra Color, safely eject and the installer will run and your KLC will restart. Once it has restarted copy the attached file into the .adds/nm directory on your KLC which will supply some basic menu functions for NickelMenu. The doc file you will find in the .adds/nm is the documentation file for NickelMenu's functions if you want to look at adding additional options.
After the above, you can tap on the NickelMenu item on the Home and Books screen or the ... menu in the reader screen menu to enable/disable screenshots at a tap.