It's a bit confusing I'll admit. Skins and palettes are classified as the same thing so if you unlock a color palette for a skin you don't have, it will unlock that skin.
Invasions: By playing invasions, you will open chests that have skins, palettes and gear. Every sub boss on each map will have an unlockable skin, and the final SEASONAL boss has an unlockable skin (Scorpion in this season).
Story Mode: There are color palettes for default skins as well as character specific gear in the story mode that you unlock every fight.
Daily Quests: You can unlock color palettes through the daily quests.
The Shrine: It's random, but the coins you need to use for the shrine you can't use anywhere else, so you can earn skins and gear randomly through it.
Character Mastery: You get gear pieces as well as color palettes through character mastery.
Seasonal Store: Every season has a store that has skins, palettes, as well as gear for every single character on the roster. You can unlock them with the currency you get from playing invasions, it's free.
Premium Store: With dragon crystals, you can unlock skin and gear bundles (costs money). Note that some of these skins can be unlocked through the shrine for free.
Kameos: You unlock palettes and skins for them through Kameo mastery.
If y'all don't wanna read, I made a video showing everything.
Invasions: By playing invasions, you will open chests that have skins, palettes and gear. Every sub boss on each map will have an unlockable skin, and the final SEASONAL boss has an unlockable skin (Scorpion in this season).
Story Mode: There are color palettes for default skins as well as character specific gear in the story mode that you unlock every fight.
Daily Quests: You can unlock color palettes through the daily quests.
The Shrine: It's random, but the coins you need to use for the shrine you can't use anywhere else, so you can earn skins and gear randomly through it.
Character Mastery: You get gear pieces as well as color palettes through character mastery.
Seasonal Store: Every season has a store that has skins, palettes, as well as gear for every single character on the roster. You can unlock them with the currency you get from playing invasions, it's free.
Premium Store: With dragon crystals, you can unlock skin and gear bundles (costs money). Note that some of these skins can be unlocked through the shrine for free.
Kameos: You unlock palettes and skins for them through Kameo mastery.
If y'all don't wanna read, I made a video showing everything.