where is the documentation ?

[Jacques]

Where is the documentation please ?

[Hans Raaf]

In the README. What is the problem?

  // The indent color if the number of spaces is not a multiple of "tabSize".
  "indentRainbow.errorColor": "rgba(128,32,32,0.6)"

  // The indent color when there is a mix between spaces and tabs.
  // To be disabled this coloring set this to an empty string.
  "indentRainbow.tabmixColor": "rgba(128,32,96,0.6)"

https://github.com/oderwat/vscode-indent-rainbow#hiding-error-highlighting

Duplicate of #149