I just tried to install the AT&T OS on my unlocked 8700g (origionally with T-Mobile) and now the home screen is black and white with little icons. Has this happened to anybody else and is there a way to fix it. Thanks in advance for any help!

Try this => What to do next if Jl Cmder will not connect and wipe - BlackBerryFAQ

if that fails try this=> How do I "wipe" my 8700 device using Jl Cmder? - BlackBerryFAQ

then finally this
=>How do I upgrade the OS on my BlackBerry? - BlackBerryFAQ

I've seen this on my BB once before. Locate the icon that looks like a toolbox, and says Options. (or press O if you have keyboard shortcuts enabled.) then from the menu that appears, select theme, and then select some theme. It appears that the BB will do this if there is no theme file selected. (Don't ask me why)

I agree with moleman. It's not serious. You have no theme installed and it's reverted back to it's basic theme. Simply locate the swiss army knife icon (tools) and go to Themes and select a theme.

All that happened is you had a theme on the device prior to the upgrade that isn't on the device after the upgrade. The BB doesn't know what theme to load so it loads none.

I hope you didn't wipe the device as suggested above.