If you haven't closed the image yet, you can go to a step in your History panel before you made the change. If you have already closed the image, you cannot undo the change, as Photoshop does not save your History.
Note: if the mode change was from RGB to CMYK, or vice versa, you can always convert back, however, you will never get back exactly what you had before the first conversion.
There are many different ways to Undo in Photoshop. Ctrl + Z is keyboard shortcut for Undo last operation, Ctrl + Alt + Z is Undo keyboard shortcut. You can Undo and from Edit > Undo or from HISTORY panel (Window > History).
To revert everything you have done to beginning, in other words to undo everything and go back to state when you have opened image in Photoshop.
In Photoshop the Command (Apple) key + Z will Undo your last action using the Option (Alt) key with Command + Z will repeatedly Undo your previous actions - effectively scrolling back up through the History palette.
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ctrl+Z to undo , if you selected more than one thing ctrl+shift+Z can go back further steps if you where doing something more advanced also that can be used in anything you can do to undo in photoshop.
You mean Color Mode? Changing how Photoshop treats and displays colors in an image.
Full Screen Mode: the F11 key toggles Full Screen Mode on and off.
color layers is simply color layers
You ca use "CTRL and Z" together and it will take you back one step at at a time depending how many are in the history
Probably because you work in Grayscale mode. Go to Image > Mode and click RGB Color.
When the overtype mode is turned on, new text replaces existing text as you type rather than inserting it. This means that if you accidentally overwrite text, you can use the undo function (typically Ctrl+Z) to revert to the previous state, restoring the overwritten content. However, the ability to undo depends on how many actions your software retains in its undo history. Always check your specific application for its capabilities regarding undoing edits in overtype mode.
When you power up the system before it starts there is an opportunity to push F8 usually that will let you into safe mode operation. Bring it up in safe mode and see if you can undo what you have doen and then restart. System restore will only usually undo installed programs and not single files that you may have downloaded, but as before try safe mode. If XP will not undo your Restore, try going back to a Restore or Check point that was created just before the Restore point that you originally selected and Restore from one of these two points. Michael R. Palazzo