in conclusion

① Duplicate the underpainting cel or underpainting folder and clipping it to the underpainting

 

② Mask the duplicated folder and place the adjustment layer inside the folder

 

③ Make sure that the duplicated folder has only the shaded color. In my case, I wanted to set only the skin shadow to a specified color, so I separate the folders into skin and others.

④ Once you have created only the shadow color, select the mask attached to the folder for each cell for anime or the folder for all shadow colors for illustrations and delete

 

⑤ All you have to do is write the line you want to paint the shadow on the mask, set the bucket tool's reference destination to the line art layer, and then paint it on the mask.

bonus

If you want to reduce the number of steps a little, or just use the adjustment layer mask.

 

① Set the bucket settings to “All layers” and “Do not refer to locked layers” for the layers you do not want to refer to.

 

② If there are gradient layers such as cheeks or hair, it will get in the way, so lock it.

 

③ Draw a line on the mask of the adjustment layer and fill it with a bucket

lastly

At the moment, I feel like this is the way to go if you really want to save time when painting animation shadows using adjustment layers.

 

If I find a better way, I'll post a new one.