Is there a way for only lineart to show when onion skin is enabled?
I have trouble figuring out where smaller details are with just block colors.
If you use the Drawing view that will work quite well just by not enabling the Preview (you’ll see only the selected sublayer on the onion skin).
In the Camera View it doesn’t work quite in the same way. You can click on the Current Drawing on Top and you’ll see only Line or Colour Art, but when activating the onion skin even when the Line Art is selected you’ll see red and green colour fills. This can be changed in Preferences > Drawing > Onion Skin Render Style and then select Outline only. You won’t get a regular line (just the outline of the line) but at least you will get rid of the undesired colour fill.
I would just switch to the Drawing View when necessary.
(This is the behaviour in Harmony 15, I don’t know if something was changed in 16)