[FEATURE] Support custom keyword highlighting/coloring in chat messages (not just in code blocks)

Preflight Checklist

• [x] I have searched existing requests and this feature hasn't been requested yet
• [x] This is a single feature request (not multiple features)

Problem Statement

Currently, Claude Code's chat interface only supports syntax highlighting inside code blocks (triple backticks). Regular conversation text is rendered as plain Markdown without any ability to highlight or color specific keywords.

This limitation makes it difficult to quickly scan and understand long technical conversations. Important terms, commands, file paths, status indicators (e.g. error/warning/success), or domain-specific keywords are hard to distinguish visually.

While code blocks already have good syntax highlighting, the lack of similar visual enhancement in normal chat messages reduces readability and efficiency during debugging, code review, and multi-project work.

Proposed Solution

Add support for custom keyword highlighting/coloring in regular chat messages (outside of code blocks).

Desired behavior:

• Allow users to highlight or apply color to specific keywords in the conversation.
• Ideally support a simple way to define keywords and their colors (either through configuration or lightweight inline syntax).
• This should work seamlessly alongside the existing Markdown rendering and code block syntax highlighting.

This feature would significantly improve the visual scanning experience in long technical discussions without requiring users to wrap everything in code blocks.

Alternative Solutions

_No response_

Priority

Medium - Would be very helpful

Feature Category

Interactive mode (TUI)

Use Case Example

Example scenario:

1. I'm working on a complex backend service and frequently discuss code structure, configuration files, and debugging steps with Claude Code.
2. During a long conversation, I often mention specific keywords like file names (config.yaml, main.go), important functions, error states (error, warning, success), or command names.
3. Currently, these keywords blend into the normal text and are hard to quickly locate when scrolling back through the conversation.
4. With keyword highlighting support, I could define or automatically highlight these important terms, making it much faster to scan previous messages and understand the context.
5. This would significantly improve readability and reduce the time spent re-reading long chat histories.

Additional Context

• This feature would enhance the existing Markdown rendering in the chat interface.
• Code blocks already support syntax highlighting, so extending similar visual capabilities to regular text would be a natural improvement.
• The feature should ideally allow users to either:
• Manually highlight keywords, or
• Configure a list of keywords with assigned colors.
• This is primarily a UI/UX improvement rather than a core CLI functionality.
• Similar keyword highlighting features exist in many modern IDEs and chat tools (e.g., VS Code, Slack, Discord) and greatly improve information scanning efficiency.