add look_in file to color file set

When I use sugarcube-color only, I got an error.
Fix dependency.

```
gem 'sugarcube', :require => 'sugarcube-color'
```

```
:black.uicolor

symbol.rb:12:in `uicolor:': uninitialized constant Symbol::SugarCube (NameError)
=> #<NameError: uninitialized constant Symbol::SugarCube>
```