How to fix blank/white Cydia icon for 4.2.1 tethered jailbreak
I have had a few reports from our readers that after performing a 4.2.1 jailbreak with redsn0w they restarted their devices only to find that the jailbreak had worked but their Cydia icon was just a blank white icon. There is a very simple fix for this that I will explain below.
Most of you should be familiar with the Redsn0w process, if not take a look at our tutorials section and read a different tutorial on Redsn0w, they mostly all operate in the same manner just with different features and functions. After you have downloaded Redsn0w 0.9.6b4 open it up and browse to your factory 4.2.1 firmware file. If you don't already have the firmware file saved to your hard drive you can redownload it here.
After you have browsed to the 4.2.1 firmware file and Redsn0w has patched it and you get to the option screen. Select ONLY the option that says "Just Boot Tethered" Then select next and Redsn0w will instruct you to put your device into DFU mode.
After you have put your device into DFU mode, Redsn0w will do it's thing and when your device restarts you should have your Cydia icon back. Please let us know if you experience any difficulties or if this fix worked for you!