ColoredKnob jailbreak app lets you change the colour of your iPhone slide to unlock slider . You can replace the boring old gray slider with red and green slider buttons (as shown below) . The jailbreak app is available for free in the BigBoss repository . Follow the steps below to install the slider customizing tweak from Cydia .
Update : Colorknob has been updated with more colours like Blue , Yellow , Pink , Violet , Black , Light Blue and Lock icon . All this free of charge .
Supported on iPhone 4S , iPhone 4 , iPod Touch 4 , iPod Touch 3G .
You have to first jailbreak your iPhone and iPod Touch and install Cydia. In Cydia go to the Search tab and type ColoredKnob . Tap on the first result and install .
Fore more tips and tweaks read . Other LockScreen tweaks