Update masks.html

[akibi90]

Add black color in the chat when you roll a dice

Submission Checklist

Required

• The pull request title clearly contains the name of the sheet I am editing.
• The pull request title clearly states the type of change I am submitting (New Sheet/New Feature/Bugfix/etc.).
• The pull request makes changes to files in only one sub-folder.
• The pull request does not contain changes to any json files in the translations folder (translation.json is permitted)

Changes / Description

Add black color in the chat when you roll a dice

[roll20deploy]

Character Sheet Info Roll20 Internal Use only.