[Added] Support for 26.1.x and 26.2, where this update has been tested.
[Added] You can now use MiniMessage in every message (boss bar, title, subtitle). Gradients, rainbow, hex colors, all of it. Your old & codes still work too.
[Added] PlaceholderAPI support in titles and subtitles. Just drop in any %placeholder%. Only works if you have the plugin installed.
[Changed] Now needs Paper 1.18.2 or newer (Java 17). Spigot is no longer supported, so use Paper forks instead.
[Changed] SayanVanish updated to 1.5.0 API.
[Changed] Cleaned up and simplified a bunch of code.
[Removed] Old <SOLID:..>, <GRADIENT:..> and <RAINBOW1> tags. Use MiniMessage now, examples are below.

Code (YAML):

  # Legacy & codes and MiniMessage both work, mix them however you like.
  #
  # Colors:      &a &b &c ... or <green> <red> <gold> ...
  # Formatting:  &l &o &n ... or <bold> <italic> <underlined> ...
  # Hex:         &#00FFD3 {#00FFD3} <#00FFD3>
  # Spigot hex:  &x&0&0&F&F&D&3
  # Gradient:    <gradient:#2C08BA:#028A97>text</gradient>
  # Rainbow:     <rainbow>text</rainbow>
  # Placeholders needs PlaceholderAPI

  BossBarMessage : "<gradient:#00FFD3:#028A97><bold>You are invisible</bold></gradient>"

If you know of any bugs or would like to see support for any other Vanish plugin, feel free to post in the discussion. I will also be glad for positive reviews.