Yo man, I have the answer for you but not the time to type it up nice with images properly.
Onion skin in GG def seems weird at first and can be confusing.
Once you know what it wants its all good tho.
For the most basic use:
+ go to Frame Properties of any frame
+ drop down the menu that says Current Frame
+ select the All Frames option
+ Onion Skin in GG requires the frames you want to skin to have Frame Transparency active
+ you will only be able to see the onion skin thru the set Transparent Color
+ look at the checkbox next to Transparency
+ the checkmark will be GRAY because selecting All Frames assumes a neutral setting --> no change
+ click the GRAY checkmark so that it becomes a BLACK checkmark --> this means you have turned on Transparency for all frames
+ when you turn on Transparency from an off or neutral state it will set the Transparency Color based on the color of the pixel in the top left of your canvas --> most likely your background color which is what you want, but if you have some other pixels in the top left it will fuck you over so be careful
+ if GG does not auto select the correct color you want to see thru you need to do it manually by clicking the color block or eyedropper below
+ click OK
+ now turn on Onion Skin by clicking the little green dood button
+ the drop down arrow next to it will let you set Next Frame, Back Frame, or Both
+ you can only view -1 +1 frame in GG, unlike Flash where you can choose a range, or other software that lets you set specific frames to view, its limited but thats what you get deal with it
+ if the Opacity of the Onion Skin is not to your liking you can adjust it in File --> Preferences --> View tab --> Onion Skin --> Opacity slider
+ also I recommend you turn on Loop the First and the Last checkbox --> this will show the first frame as onion skin if you have the last frame selected --> wraps the animation
+ on that note I also recommend you go to the Frame tab and also turn on Loop First and Last --> will make it so if you have the last frame selected and you press Next Frame you will go to the first frame and vice versa --> scrubbing frames loops
And there you go, that's the big messy answer.
So I don't have time to type it out cleanly.
If you still cant get it, pm me when you're around and I can show you on stream how to do it.
