You can use the following to fully define the comment colors globally. You do not have to do one for each language!
settings.json
"editor.tokenColorCustomizations": {
"comments": "#636363",
"textMateRules": [{
"scope": "punctuation.definition.comment",
"settings": {
"foreground": "#636363",
}
}]
},
Notice I omitted the language, ie: .php, from the end of the scope line.
This will do both the beginning/end of the comment block, and the comment itself. I was baffled when I changed my comment colors and the /** and */ where not changed. This solved it and made the comments all one color.