Snippet from modified dot.tmLanguage file.

gistfile1.json

{
    "fileTypes": [
        "dot",
        "DOT"
    ],
    "foldingStartMarker": "\\{",
    "foldingStopMarker": "\\}",
    "keyEquivalent": "^~G",
    "name": "Graphviz (DOT)",
    "patterns": [
        {
            "begin": "\\s*(label)\\s*=\\s*(<)",
            "beginCaptures": {
                "1": {
                    "name": "support.constant.attribute.node.dot"
                },
                "2": {
                    "name": "punctuation.definition.label.begin.dot"
                }
            },
            "end": ">",
            "endCaptures": {
                "0": {
                    "name": "puncutation.definition.label.end.dot"
                }
            },
            "name": "meta.label.dot",
            "patterns": [
                {
                    "include": "text.html.basic"
                }
            ]
        },
        {
            "match": "\\b(node|edge|graph|digraph|subgraph|strict)\\b",
            "name": "storage.type.dot"
        },
        {
            "match": "\\b(bottomlabel|color|comment|distortion|fillcolor|fixedsize|fontcolor|fontname|fontsize|group|height|label|layer|orientation|peripheries|regular|shape|shapefile|sides|skew|style|toplabel|URL|width|z)\\b",
            "name": "support.constant.attribute.node.dot"
        },
        {
            "match": "\\b(arrowhead|arrowsize|arrowtail|color|comment|constraint|decorate|dir|fontcolor|fontname|fontsize|headlabel|headport|headURL|label|labelangle|labeldistance|labelfloat|labelcolor|labelfontname|labelfontsize|layer|lhead|ltail|minlen|samehead|sametail|style|taillabel|tailport|tailURL|weight)\\b",
            "name": "support.constant.attribute.edge.dot"
        },
        {
            "match": "\\b(bgcolor|center|clusterrank|color|comment|compound|concentrate|fillcolor|fontname|fontpath|fontsize|label|labeljust|labelloc|layers|margin|mclimit|nodesep|nslimit|nslimit1|ordering|orientation|page|pagedir|quantum|rank|rankdir|ranksep|ratio|remincross|rotate|samplepoints|searchsize|size|style|URL)\\b",
            "name": "support.constant.attribute.graph.dot"
        },
        {
            "begin": "\"",
            "beginCaptures": {
                "0": {
                    "name": "punctuation.definition.string.begin.dot"
                }
            },
            "end": "\"",
            "endCaptures": {
                "0": {
                    "name": "punctuation.definition.string.end.dot"
                }
            },
            "name": "string.quoted.double.dot",
            "patterns": [
                {
                    "match": "\\\\.",
                    "name": "constant.character.escape.dot"
                }
            ]
        },
        {
            "captures": {
                "1": {
                    "name": "punctuation.definition.comment.dot"
                }
            },
            "match": "(//).*$\\n?",
            "name": "comment.line.double-slash.dot"
        },
        {
            "captures": {
                "1": {
                    "name": "punctuation.definition.comment.dot"
                }
            },
            "match": "(#).*$\\n?",
            "name": "comment.line.number-sign.dot"
        },
        {
            "begin": "/\\*",
            "captures": {
                "0": {
                    "name": "punctuation.definition.comment.dot"
                }
            },
            "end": "\\*/",
            "name": "comment.block.dot"
        }
    ],
    "repository": {
        "doublequotedString": {
            "begin": "\"",
            "beginCaptures": {
                "0": {
                    "name": "punctuation.definition.string.begin.dot"
                }
            },
            "end": "\"",
            "endCaptures": {
                "0": {
                    "name": "punctuation.definition.string.end.dot"
                }
            },
            "name": "string.quoted.double.dot",
            "patterns": [
                {
                    "include": "#entity"
                },
                {
                    "include": "#bare-ampersand"
                }
            ]
        },
        "singlequotedString": {
            "begin": "'",
            "beginCaptures": {
                "0": {
                    "name": "punctuation.definition.string.begin.dot"
                }
            },
            "end": "'",
            "endCaptures": {
                "0": {
                    "name": "punctuation.definition.string.end.dot"
                }
            },
            "name": "string.quoted.single.dot",
            "patterns": [
                {
                    "include": "#entity"
                },
                {
                    "include": "#bare-ampersand"
                }
            ]
        },
        "tagStuff": {
            "patterns": [
                {
                    "captures": {
                        "1": {
                            "name": "entity.other.attribute-name.namespace.dot"
                        },
                        "2": {
                            "name": "entity.other.attribute-name.dot"
                        },
                        "3": {
                            "name": "punctuation.separator.namespace.dot"
                        },
                        "4": {
                            "name": "entity.other.attribute-name.localname.dot"
                        }
                    },
                    "match": " (?:([-_a-zA-Z0-9]+)((:)))?([-_a-zA-Z0-9]+)="
                },
                {
                    "include": "#doublequotedString"
                },
                {
                    "include": "#singlequotedString"
                }
            ]
        },
        "xmlPatterns": {
            "patterns": [
                {
                    "begin": "(</?)(?:([-_a-zA-Z0-9]+)((:)))?([-_a-zA-Z0-9:]+)",
                    "captures": {
                        "1": {
                            "name": "punctuation.definition.tag.begin.dot"
                        },
                        "2": {
                            "name": "entity.name.tag.namespace.dot"
                        },
                        "3": {
                            "name": "entity.name.tag.dot"
                        },
                        "4": {
                            "name": "punctuation.separator.namespace.dot"
                        },
                        "5": {
                            "name": "entity.name.tag.localname.dot"
                        }
                    },
                    "end": "(/?>)",
                    "endCaptures": {
                        "1": {
                            "name": "punctuation.definition.tag.end.dot"
                        }
                    },
                    "name": "meta.tag.dot",
                    "patterns": [
                        {
                            "include": "#tagStuff"
                        }
                    ]
                }
            ]
        }
    },
    "scopeName": "source.dot",
    "uuid": "1A53D54E-6B1D-11D9-A006-000D93589AF6"
}