WARNING on line 2, column 5 of /sass/spec/libsass-issues/issue_2155/input.scss:
You probably don't mean to use the color value `#ff0' in interpolation here.
It may end up represented as #ffff00, which will likely produce invalid CSS.
Always quote color names when using them as strings (for example, "#ff0").
If you really want to use the color value here, use `"" + #ff0'.

Error: Invalid CSS after "&.": expected class name, was "#ff0"
        on line 2 of /sass/spec/libsass-issues/issue_2155/input.scss
  Use --trace for backtrace.