For firmware 1.1.4 only:
The PNG file you are looking for is called "Other-ver114_171.png" and it is packaged in the file /System/Library/Frameworks/UIKit.framework/Other.artwork
You have to extract all of the PNG files using this tool:
ArtWorker
You can then edit the graphics and replace them as necessary.
See this link for more information: (Post about v1.1.1 artwork files)
Massive list of .artwork files and what they edit on the phone
To make things easier for the OP, I have taken an original 1.1.4 "Other.artwork" file and blanked out the "Other-ver114_171.png" file so that the gradient behind the clock will be invisible.
1) Download the attached zip file.
Other.artwork with transparent gradient for v1.1.4.zip
2) Unzip "Other.artwork" file.
3) Upload "Other.artwork" file to the /System/Library/Frameworks/UIKit.framework directory on your v1.1.4 iPhone. It will not work on any other firmware version because each firmware version has different artwork files. Remember to backup your original file first.
4) Reset Springboard or reboot iPhone.
Let me know if you have any questions regarding this process, as I have learned a bunch about it in the past few hours.
Good Luck.