"slate grey" meaning in English

{
  "forms": [
    {
      "form": "slate greys",
      "tags": [
        "plural"
      ]
    }
  ],
  "head_templates": [
    {
      "args": {
        "1": "~"
      },
      "expansion": "slate grey (countable and uncountable, plural slate greys)",
      "name": "en-noun"
    }
  ],
  "lang": "English",
  "lang_code": "en",
  "pos": "noun",
  "senses": [
    {
      "alt_of": [
        {
          "word": "slate gray"
        }
      ],
      "categories": [
        {
          "kind": "other",
          "name": "English entries with incorrect language header",
          "parents": [
            "Entries with incorrect language header",
            "Entry maintenance"
          ],
          "source": "w"
        }
      ],
      "examples": [
        {
          "ref": "2014 June 20, Daniel Taylor, “World Cup 2014: Uruguay sink England as Suárez makes his mark”, in guardian.co.uk",
          "text": "England were even more vulnerable under the slate-grey skies of Sáo Paulo than they had been in the searing heat of Manaus.",
          "type": "quotation"
        }
      ],
      "glosses": [
        "Alternative form of slate gray"
      ],
      "id": "en-slate_grey-en-noun-vk21Bp~6",
      "links": [
        [
          "slate gray",
          "slate gray#English"
        ]
      ],
      "tags": [
        "alt-of",
        "alternative",
        "countable",
        "uncountable"
      ]
    }
  ],
  "word": "slate grey"
}

{
  "forms": [
    {
      "form": "slate greys",
      "tags": [
        "plural"
      ]
    }
  ],
  "head_templates": [
    {
      "args": {
        "1": "~"
      },
      "expansion": "slate grey (countable and uncountable, plural slate greys)",
      "name": "en-noun"
    }
  ],
  "lang": "English",
  "lang_code": "en",
  "pos": "noun",
  "senses": [
    {
      "alt_of": [
        {
          "word": "slate gray"
        }
      ],
      "categories": [
        "English countable nouns",
        "English entries with incorrect language header",
        "English lemmas",
        "English multiword terms",
        "English nouns",
        "English terms with quotations",
        "English uncountable nouns"
      ],
      "examples": [
        {
          "ref": "2014 June 20, Daniel Taylor, “World Cup 2014: Uruguay sink England as Suárez makes his mark”, in guardian.co.uk",
          "text": "England were even more vulnerable under the slate-grey skies of Sáo Paulo than they had been in the searing heat of Manaus.",
          "type": "quotation"
        }
      ],
      "glosses": [
        "Alternative form of slate gray"
      ],
      "links": [
        [
          "slate gray",
          "slate gray#English"
        ]
      ],
      "tags": [
        "alt-of",
        "alternative",
        "countable",
        "uncountable"
      ]
    }
  ],
  "word": "slate grey"
}