How to Shade Faster

I have to use the Freehand selection Tool to select the yellow clothing so that I can shade that yellow clothing without it reaching the other flat colors.

The problem is that this is very inpractical as I would have to select many pieces of yellow, green silver etc. to finish shading the entire piece.

Is there a better and faster way of shading many re-appearing colors?

If I wanted to select all the ‘yellow’ colours then I’d use the Contiguous Selection tool with it’s Action set to Add. Then for the areas I wanted, I’d click on them and keep clicking until I picked up all of it:

If the Fuzziness is too low, you pick up little bits and pieces. If the Fuzziness is too high then you might go outside the required area but you have black lineart acting as a boundary so that shouldn’t be a problem with this particular image.
If something you don’t want is picked up then you can set Action to Subtract, reduce Fuzziness and remove it a bit at a time, or you can switch to the Feehand selection and use that with Subtraction to remove unwanted areas, or add wanted areas, whatever.

If you’ll be doing a lot of highlighting, shading, HSV adjustment, etc on different selected areas, it’s a very good idea to make a selection and then store that Global Selection mask as a Local Selection Mask by dragginbg it onto a ‘storage layer’ then do that for further different selections.
Then, to work on a particular selection, you drag it from the storage layer onto the working layer and do the highlight, whatever on the working layer.
Drag that local selection mask back onto the storage layer when you’ve finished working with it.

There are various ways…I know some people use the Split Layer functionality to turn their flat coloring into separate layers for each color. You can then select the parts with “Select Opaque” (usually by pressing Ctrl and clicking on the layer thumbnail, which does not change layer focus).

That does take too much space in the layers docker for my taste though.

What I often do is give the flat color layer (often just the random colors from G`MIC “colorize lineart” filter) a color label and set the Contiguous Selection Tool to sample that label, then you can use the tool without having to switch layers, and on top can adjust feathering/grow as needed.

Does the Split Layer functionality option only appear for colorize mask layers? I already converted my CM layer into a paint layer which explains why I can’t turn that mentioned PL into a “Split Layer”.

nevermind, I found it but there is an option saying “ignore opacity”. What does this mean? Is it reversable?

When I try to split my Color Paint Layer, the mouse icon stays in a blue circle and the color paint layer does not convert even after ~5 minutes.

If your paint layer has gradients on it, as when you’ve been doing shading, there will be many different individual colours.
It’s better to use Split Layer with an image that contains few colours, i.e. a flat colouring layer.

Edit:Add: Having said that, I have no problem splitting the image you posted, with a Fuzziness of 30:

i turned off the shadows layer AND unchecked the “sort layers by amount of non-transparent pixels” option in the prompt that appears after clicking split layers. One of these options worked and it may be because I had to make the shadows layer invisible

Ideally, you’d use Split Layer on the flat colouring layer and work forward from there with shading, highlighting, etc.

I split my flat color layer into layers with each color but “grey” for example has apricot and silver in it. How do I fix this?

Sounds like an issue with fuzziness. The layer split algorithm isn’t the smartest, it works best with solid colors and hard edges, so you’d want to use it on a colorize mask before doing anything else with it.

As mentioned, it’s not my main way to select parts, I only keep a few things apart, like character skin, all clothing, maybe hair, so I do that manually.

I just remember that on my last project using lineart (this one) I put my lineart layers in a group (including a helper layer that I discarded when finshed, to close some gaps), assigned a color label to the group and set the contiguous selection tool to that label.

And I set a keyboard shortcut for that tool too, because I obviously used it a lot to select areas to shade.