@ Egor: It is a really simple template - a safe colour/easy for the eyes background, few technical colours and a layer stack for the layer colour trick, reference and work. Those 27 necessary layers are hidden within FOR CYAN generator layer.

EDIT: no matter how I try, and from what browser, the template file does not upload.

Thanks for the extended reply!
I am eager to take a look at your template file. I understand the method you have described, but I’d like to see it for real.

Totally agree on Fn and actions in general.

@Egor I can't say I love actions, but I do use them. The reason why this workaround fits my workflow better is that I use multiples of colour coded layers for different aspects of my work. Usually 3-5 different, repetitive colours in a file, that at the end of the project contains dozens of top level layers, each with dozens nested sublayers in it. So I would need 5 shortcut actions to replicate this flow. And there is no cumbersome stack, as those 27 layers can be sublayers hidden inside of one of those "generator" layers. So my template file now consists of reference layer, work layer and 2-5 generator layers. It is neat enough and very convenient to use. The additional problem with F-key assigned actions is that on a laptop this requires using awkwardly located Fn button (so using two hands for half of F-keys) and differs significantly from using the same F-keys on a full sized keyboard, messing up with my muscle memory. An alternative of setting up the keyboard to use F-keys as default collides with just too much other everyday uses of the keyboard.

Łukasz, I strongly encourage you to start loving actions and scripts :) They save so much time and nerves, and I have no idea how broken I’d be mentally without these and various plugins. One key against of a shaky stack of 27 layers workaround is not even a fair comparison.
So the way is to use these and keep pushing the team with votes.
And thanks for posting and commenting, we need more of this here to make this really going.

A convenient trick I just came up with to get multiple layers with a desired colour via + icon in layers panel: make a layer with a colour PRECEDING the one you want and move it to the bottom of the stack. When you select this layer and click on + icon, the new layer will have the next colour from the list - your desired one. It is still a workaround, but fits my workflow well enough without having to get accustomed to F-key script workflow. EDIT: ech... this trick only works if you have more than 27 layers in your document, so you run out of the predefined colours sequence. Illustrator is a strange beast indeed. But since you can put layers into other layer, a template for this trick at least doesn't look strange.

To solve a problem with a custom color for new layers (https://illustrator.uservoice.com/forums/333657/suggestions/41592469) I wrote a very simple script which always creates a blue layer for me. It can be modified to have any other color you want, including black.
I put in the action and hacked it instead of default Cmd/Ctrl+L with a remapping app (you it can be simply run with an F-key instead).
You can download the script here: https://dl.dropboxusercontent.com/s/78vzy3u79e6erxu/New%20Layer%20Custom%20Color.jsx

Why there is no default layer colour setting boggles my mind. It has been requested since forever (at least the last 15 years that I work in AI) and it shouldn't really be all that hard to implement. Ideally, there should be an option to set custom default colour and a checkbox to either use this default for every new layer or to cycle through the list of colours. The list itself should also be customizable. I'm seriously photosensitive epileptic and as it is now I have to tripple check to always manually set safe layer colours for the content, to prevent accidental exposure to high colour contrast lines pattern when I "select all" on some dense design.

We should absolutely be able to set our own default colors. Similar features exist in After Effects and have for some time, and changing them to my preferences was amazing. Silly that we can't do it in Illustrator, it'd be especially helpful for motion designers such as myself who would appreciate keeping Illustrator & AE layer colors the same between apps.

Like DigitalDesignDude, I'm on a recent version (25.3.1) and I'm still seeing yellow.
Actually removing yellow would be a great start, implementing some sort of user control over the auto layer colors would be ideal.

I'm using Illustrator ver 24.3 and the Yellow layer option is still present for symbol layers and can't be changed as can be seen in the below youtube video capture of my experience.

https://youtu.be/_a6U_PoiyOs

I like the range of layer colors from light to dark in the options, but it's annoying that I can not set 1 layer color in my preferences in AI. It sucks that everytime I draw on a layer with a black outline that the auto selected layer colors are black, dark purple, dark blue etc. It would be cool to program AI to auto select contrasting layer colors for light stroke/fill or a dark stroke/fill paths.

TLDR: check boxes with the ability to turn off the current colors to prevent them appearing

I work with black strokes, which renders the black layer pointless, and frustrating. I also find the same for yellow. Rather than having to delete the layers all the time (or change the color manually which doesn't necessarily solve the issue), it would be nice if we could choose out default layer colours in a preference panel. even a set of check boxes with the ability to turn off the current colors would be fine.

the yellow layer color has somehow become default for editing a symbol and it's impossible to work with. Anyone know how I can swap it to any other layer color permanently?

I aggree with Anom - Black is the worst color - can't see anything. I work on dark backgrounds usually, so I prefer light colors to dark. Ability to have a custom set would be very welcome. Or just the ability to delete black/yellow would be great.

Yup Yellow is the worst

Beg to differ! BLACK is the worst layer color ever!! but yellow is pretty bad too ;)

If you are setting up the same type of file all day long(say it always has 8 layers, and 6 default colors, etc. etc) you can build a file that is your base line starting file(what you would like the file to look like when you created a new doc) and either A. save it as a new document profile B. save it over the current default new doc profile(usually called 'print') or C. Save it as an illustrator template.

Bad news is that this will not stop illustrator from creating layers that default to the color yellow. good news is you shouldn't have to deal with changing it in EVERY file you build, and hopefully it will push it way down in the auto order...

hope this helps!

Please remove layer colors that lack contrast based on the currently used foreground color, or some predictive algorithm of last used colors. When CREATING A NEW LAYER AND working using black lines (most common) colors like yellow, black, greys, etc. are almost totally useless because of the lack of contrast. It's just one more tedious hassle to have to double click and change the layer color back to something like pink or blue so you can actually see what you are working on.

Other than just removing the yellow layer color, how about making it a preference/option to have all new layers with the same light blue (or custom color)?

ONLY dark colours should be there. NO Yellow, light Green, light Pink.
Please fix.

light colors like yellow should NEVER be in the list of auto created layer colors! At least just move the yellow color to the end of the line. Worst layer color ever.