Visuals

Visual symbols affect only the appearance of the world, not any gameplay factors. The category is required but can appear many times. Most of these are symbols which simply change the color of part of the environment. Each of these has a "Natural" version which takes no modifiers, and a "custom" version which takes a color (ground colors) or gradient (sky colors) as their only modifier. There are also a couple of extra sky effects. Note that sunset colors (including sunrise, moonset, moonrise) have their own symbol (Does the global version coulnt as a Visual?), while Stars and Lightning take their colors from a modifier.

Specifying the same color scheme (e.g., Foliage Color) twice in a book is an error.

Ground colors take only a color modifier (except Natural versions). Some Biomes can also affect the result.
 * Foliage Color: Not all trees may be afffected, notably mod trees.
 * Natural Foliage Color
 * Grass Color: May be affected by biomes (e.g. Swamps)
 * Natural Grass Color
 * Water Color: Minecraft imposes a blue tint on water.  "White, Water color" will give the vanilla color, "Pink, Water color" will give a grayish color.
 * Natural Water Color

Sky Colors: The non-Natural symbols take a Gradient.
 * Fog Color:
 * Natural Fog Color
 * Cloud Color
 * Natural Cloud Color
 * Sky Color
 * Natural Sky Color
 * Night Sky Color: Shows when no sun is in the sky.
 * Natural Night Sky Color

Visual Effects:
 * Boundless Sky: No visible horizon, pupular for void and island worlds.
 * Rainbow: A rainbow will show in the sky.  Takes Direction modifiers.