Why does 'silver' needs quotation marks within Object Literals?

It says that we can omit the quotation marks if there is no space. Why does silver still need quotation marks and color not?

https://www.codecademy.com/paths/web-development/tracks/web-dev-js-arrays-loops-objects/modules/learn-javascript-objects/lessons/objects/exercises/objects

Hello, @remogirard7746549799.

Welcome to the forums!

In the example, color is a key. Keys that don’t contain special characters like spaces can have the quotation marks omitted. The values, if they are strings, always require quotation marks. For quick reference, here is a screenshot from the lesson:
image

Remember that object properties are made of key: value pairs. Here are some more examples showing the use of quotation marks in an object:

const dog = {

  name: 'Rover', //Key doesn't need quotes. The value is a string, so it requires quotes
  breed:  'Great Dane', //Key doesn't need quotes. The value is a string, so it requires quotes
  sex:  'Male', //Key doesn't need quotes. The value is a string, so it requires quotes
  'spayed or neutered': true, //Key contains spaces, so it requires quotes. The value is a bool, so no quotes required.
  age: 3, //Key doesn't need quotes. The value is a number, so no quotes required
  'number of tricks learned': 2 //Key contains spaces, so it requires quotes. The value is a number, so no quotes required.

};