Existing system color contexts in CSS:

• link: 🔵 LinkText, 🟣 VisitedText, 🔴 ActiveText, or (disabled) ⚫ GrayText on any background, but usually on Canvas
• canvas: CanvasText on Canvas
• button: ButtonText on ButtonFace inside ButtonBorder
• field: FieldText on Field
• highlight: HighlightText on Highlight
• mark: 🟡 MarkText on Mark
• selection: SelectedItemText on SelectedItem
• accent: AccentColorText on AccentColor

They are all implicitly influenced by color-scheme and may be influenced by it more directly in the future #9660. The accent context is also influenced by accent-color #5900.

Many generic or corporate design systems specify a limited set of base colors (or rather hues). This usually includes a primary and a secondary brand color, custom ⚫ dark/black and ⚪ light/white, but also often a neutral gray, a positive 🟢 green (confirmation action or success message), a negative 🔴 red (cancel action or failure message) and an in-between 🟡 yellow or 🟠 orange (warning message), sometimes an informative 🔵 blue or 🟣 purple. They may be used to systematically derive more tints and shades.
Operating system and browser color themes may not cover all of them, although they may be used in their GUIs, e.g. for painting icons or buttons.

The traffic light colors in particular are also frequently found in colored qualitative scales for criteria such as priority, urgency, impact, status, progress, severity, probability or risk. Many CMS contain features for admonition text boxes of various types that are indicated by color, icon or both; e.g.: 🔵 note, 🟢 tip, 🟡 warning, 🔴 caution, 🟣 important.

Although the color values may end up being the same as for Mark, LinkText, VisitedText or ActiveText, the following proposed suggestions for new (message and action) system colors are clearly semantically distinct and come in foreground / background pairs:

• informative: 🔵🟣 InfoText on Information
• positive: 🟢 ConfirmText on Confirmation
• cautious: 🟡🟠 WarnText on Warning
• negative: 🔴 FailText on Failure

(open to bikeshedding)