You can add completely customized color schemes. From the Admin Console choose App Settings and then navigate to Themes and paste a JSON array describing your desired themes like the example below:

[
  {
    "id": "hubs-default",
    "default": true,
    "name": "Hubs Default",
    "variables": {}
  },
  {
    "name": "Hubs Dark Mode",
    "id": "hubs-dark-mode",
    "darkModeDefault": true,
    "variables": {
      "loading-screen-background": "radial-gradient(50% 50% at 50% 50%, #15171B 0%, #282C31 100%)",
      "accept-color-pressed": "#21242C",
      "primary-color-hover": "#12A4ED",
      "primary-color": "#12A4ED",
      "outline-color": "#ffffff",
      "basic-color": "#3A4048",
      "basic-color-hover": "#4B5562",
      "basic-color-pressed": "#636F80",
      "basic-border-color": "#13a4ed",
      "secondary-color-pressed": "#282C31",
      "accent1-color": "#2B313B",
      "accent1-color-hover": "#5D646C",
      "accent1-border-color": "#13a4ed",
      "accent1-color-pressed": "#21242C",
      "accent2-color": "#2B313B",
      "accent2-color-hover": "#5D646C",
      "accent2-color-pressed": "#21242C",
      "accent2-border-color": "#13a4ed",
      "accent3-color-pressed": "#21242C",
      "accent3-color": "#2B313B",
      "accent3-color-hover": "#5D646C",
      "accent3-border-color": "#13a4ed",
      "accent4-color": "#2B313B",
      "accent4-border-color": "#13a4ed",
      "accent4-color-hover": "#5D646C",
      "accent4-color-pressed": "#00699E",
      "accent5-color": "#2B313B",
      "accent5-border-color": "#13a4ed",
      "accent5-color-hover": "#5D646C",
      "accent5-color-pressed": "#21242C",
      "admin-color": "#13a4ed",
      "text1-color": "#ffffff",
      "text1-color-hover": "#E7E7E7",
      "text1-color-pressed": "#DBDBDB",
      "text2-color-pressed": "#DBDBDB",
      "text3-color-hover": "#C7C7C7",
      "text3-color-pressed": "#ADADAD",
      "text2-color-hover": "#F5F5F5",
      "text2-color": "#E7E7E7",
      "text3-color": "#BBBBBB",
      "text4-color": "#BBBBBB",
      "secondary-color": "#3A4048",
      "secondary-color-hover": "#5D646C",
      "border1-color": "#3A4048",
      "border2-color": "#5D646C",
      "border3-color": "#5D646C",
      "active-color-hover": "#12A4ED",
      "active-text-color": "#2B313B",
      "background1-color": "#2B313B",
      "background2-color": "#21242C",
      "background3-color": "#3A4048",
      "background4-color": "#5D646C",
      "accept-color": "#2B313B",
      "accept-color-hover": "#5D646C",
      "accept-border-color": "#7ED320",
      "background-hover-color": "#aaaaaa",
      "input-bg-color": "#21242C",
      "tip-text-color": "#ffffff",
      "tip-bg-color": "#017ab8",
      "tip-button-color-hover": "#008bd1",
      "action-color": "#000000",
      "action-color-highlight": "#149ce2",
      "action-label-color": "#5634ff",
      "notice-background-color": "#000000",
      "toolbar-icon-selected-bg": "#ffffff",
      "toolbar-basic-icon-color": "#ffffff",
      "toolbar-basic-selected-icon-color": "#2B313B",
      "toolbar-basic-color-hover": "#ffffff",
      "toolbar-label-accent1": "#ffffff",
      "toolbar-label-accent2": "#ffffff",
      "toolbar-label-accent3": "#ffffff",
      "toolbar-label-accent4": "#ffffff",
      "toolbar-label-accent5": "#ffffff"
    }
  }
]

Use the boolean attributes, "default" and "darkModeDefault" to set a default theme from your custom themes array.

Testing your themes

Storybook, an open source tool for building UI components and pages in isolation, is very helpful in customizing themeing. To run storybook locally you can use the command npm run storybook to preview components and themes.

Theme Variables Guide

While not exhuastive, these diagrams will outline a few key variables that you can use in your themes.

Aframe Components

The in-world UI (e.g the menu you get when hovering your cursor over an object and pressing spacebar) is themed with the following variables: "action-color", "action-label-color", "action-color-disabled", "action-color-highlight", "action-text-color", "action-subtitle-color", "notice-background-color", "notice-text-color", "favorited-color".