I suggest that before you truly start to customize your Inkling (as in dressing it and changing hairstyle) you should change its color first. To do so, we are going to use material overrides. Don't worry I'll show how to use them, but pay close attention, for misusing them could really mess things up. Now, before you can use material overrides, you need to apply them first. Doing this is very simple, Just right-click the Inkling in the Animation Set Editor and press "Add Material Overrides." The material overrides have now been applied to the Inkling. Right-click the Inkling again, and this time, head to show in Element Viewer and press "Model". This will take to the Element Viewer.
Now, press + next to materials at the bottom and a sub-list of objects will appear. These are the objects of their colors you'll want to change. Let's start with the teamcolor first (This will change the eyebrows and hair if not changed yet). Press the plus next to it and you will see a colored box in its sub-list. Press that, and you will now be taken to what I call the "Color Editor". Here, you can either drag the boxes you see in the rainbow boxes, or, if your an advanced user, you can type in the numbers of the color you want it to be below the rainbow boxes. Repeat the same process for the other objects.
P.S. You'll only want to change the teamcolor, hair, and mouth (Underwear is optional)

To perform this, I reccommend FissionMetroid101's Enhanced Inklings.
Although you most likely are already using these, I just want to make sure. You will need to use the alt model. Now before you ask what those are, take a look at all the names there are for these Inklings. Each of these names are all different models. You'll want to use the ones that have alt in their names. PAY CLOSE ATTENTION TO THE NAMES! If the name has ik/alt in it, changing the hair will not work.
To change the hairstyle, just follow what this person did:
https://youtu.be/E0-fKmbVIl8
For those of you who did not get the video, what this person did was they used the alt model of Inkling Girl and brought in the hairstyle they wanted to replace the original hair with. Notice in the Animation Set Editor, they dragged the new hairstyles' bone that said "bip_head" to Inklings bone of the same name? They did that so they can lock the hairstyle to the Inkling via Zero Slider. What they did next was shrink the tentacles of the old hairstyle. You can do this by heading into the "Unknown" part of the Inkling in the Animation Set Editor, right-clicking the first bone of the hair, or in this case, the hair band root, pressing "Add Scale to Transforms", scroll down to the bottom of Unknown and here, you should see the scale control of tentacles. Click on that, and on the area below the Zero Slider, you should see a slider of the scale control you selected. Drag that all the way to the left to shrink the tentacle to the point where it disappears. Repeat the process for the other one.
Next up, the person used material overrides to truly get rid of the old hairstyle. This requires using material overrides. Repeat what you did to get to the element viewer and scroll down to materials. This time, you are going to add a new attribute. Right-click "Teamcolor_alt", head to "Add New Attribute" and press "float". You will be presented with a box that says "addNewAttibute". You'll want to replace that with "$alpha" (no quotation marks) and your Inklings old hairstyle should disappear completely. If you want to change the color of the new hairstyle, you already know what to do but this time, use the material overrides on the new hairstyle, not the Inkling.
If you have no hairstyles:
https://steamhost.cn/steamcommunity_com/sharedfiles/filedetails/?id=1746899734

We're not done yet with customizing your Inkling. Let's suppose you want to change the eye color or give it different eyebrows. Doing this will also require material overrides. Let's start with the eyes.
You should already know what to do at this point with material overrides, so I'll cut straight to what you want. Right-click one of the eyeballs, hover onto add attribute and press "string" Type in $iris and the selected eye should get a pink-and-black checkerboard pattern, but you want this to happen. Now, in the empty space next to $iris copy and paste one of these:
Blue: models\props_splatoon\inklings\inkling_eye_blue
Violet: models\props_splatoon\inklings\inkling_eye_violet
Green: models\props_splatoon\inklings\inkling_eye_green
Orange: models\props_splatoon\inklings\inkling_eye_orange
Yellow: models\props_splatoon\inklings\inkling_eye_yellow
Pink: models\props_splatoon\inklings\inkling_eye_pink
Gray: models\props_splatoon\inklings\inkling_eye_gray
Brown: models\props_splatoon\inklings\inkling_eye_brown
Octarian: models\props_splatoon\octolings\octoling_eye_octarian
If you don't want any of these eyes try one of these:
https://steamhost.cn/steamcommunity_com/sharedfiles/filedetails/?id=1364155037
https://steamhost.cn/steamcommunity_com/sharedfiles/filedetails/?id=1387021544
If none of these fit what your looking for, than your going to have to look yourself. Now, on to the eyelids.
Repeat what you did to change the eyes, except this time, press the eyelid and, while adding new attribute, type in $basetexture. The eyelids should now have a pink-and-black checkerboard pattern.
If you didn't get this then watch these videos:
https://youtu.be/at8TyRXSIyQ
https://youtu.be/whxVyks65Ak
For that last one you don't have to go through your files, just use the eyelids I supported you with.

This is possibly the most important part of customizing your Inkling. If you have not downloaded any clothes:
https://steamhost.cn/steamcommunity_com/sharedfiles/filedetails/?id=804424136
https://steamhost.cn/steamcommunity_com/sharedfiles/filedetails/?id=1646568199
https://steamhost.cn/steamcommunity_com/sharedfiles/filedetails/?id=1493448685
But you want more than just clothes, right? So...
https://steamhost.cn/steamcommunity_com/sharedfiles/filedetails/?id=1627013103
https://steamhost.cn/steamcommunity_com/sharedfiles/filedetails/?id=1634399903
https://steamhost.cn/steamcommunity_com/sharedfiles/filedetails/?id=906506002
https://steamhost.cn/steamcommunity_com/sharedfiles/filedetails/?id=685895429
https://steamhost.cn/steamcommunity_com/sharedfiles/filedetails/?id=666843949
https://steamhost.cn/steamcommunity_com/sharedfiles/filedetails/?id=1675283177
https://steamhost.cn/steamcommunity_com/sharedfiles/filedetails/?id=1285789418
https://steamhost.cn/steamcommunity_com/sharedfiles/filedetails/?id=1433710183
https://steamhost.cn/steamcommunity_com/sharedfiles/filedetails/?id=1640859575
Time to dress your Inkling! To do so, bring out your shirt, leggings, or shoes, the same way you brought out your Inkling. The same way you put your Inkling's new hairstyle on is the same way we're going to dress, just without the material overrides. Simply drag the name of the Inkling/Octoling onto the name of the "gear" and apply the zero slider.
If the "gear"" you try to put on your Inkling starts to twist and turn when you try to zero it in, there could be multiple reasons.
1. You're using an ik model
2. You have attached the wrong bones together
3. The thing you're trying to use is not compatible with the Inkling

You can change the skin tone of your Inkling. Right-click it in the Animation Set Editor and hover over to "Set Skin". This is where you change the skin tone. 0-1 is lightest, but 1 has freckles. 2-8 the skin then starts to darken. 9 is the Inkling's original ink color.

AlphaFire!'s profile
Here's some advanced customization. Let's suppose you want to make a sanitized Inkling or Octoling. To do so requires material overrides again, but this time we'll use the color attribute on the body and eyelids. Let's do the body first. Type in $color2 and the body should turn black. Now press the plus symbol and there should be a black box. Use that box to change the color of the Inklings body. Once satisfied, rinse and repeat for the eyelids. Also, you could also use this attribute on anything you wish to change the color of, allowing even deeper customization.
But what if you want to make a raging Inkling or Octoling like the one below: https://steamhost.cn/steamcommunity_com/sharedfiles/filedetails/?id=1829881684
But difference is you've changed the skin tone of the Inkling/Octoling and the color attribute is not working. This is when all those other materials saying body2 and all that come to use. You see, the number next to all of those materials are for the skins. body4 is for skin 3, eyelid7 is for skin 6. So if you've ever found yourself trying to change the eyelids if your Inkling after you've changed the skin and it appears to be doing nothing, that's because you're adding the attribute on the wrong eyelid! You're adding the attribute to the default skin. You have to add the attribute to eyelid with the number matching the skin tone number.
I hope this guide was helpful to you, let me know in the comments!