Syntax highlighting — the practice of displaying source code with different colors and styles for different syntactic elements — is so ubiquitous in modern programming that it is easy to forget it is a relatively recent innovation. Early code editors displayed monochrome text, and programmers relied entirely on indentation and naming conventions to visually parse code structure. The first widely used syntax-highlighted editor was Leif, developed at Cornell University in the 1980s, followed by Microstar's early color-coding text editors. Today, syntax highlighting is considered essential for code readability, with studies suggesting it reduces the time needed to comprehend code by 20-30%.

The technical process behind syntax highlighting involves lexical analysis — the same first phase used by compilers and interpreters. A lexer (also called a tokenizer or scanner) reads source code character by character and groups characters into tokens: keywords, identifiers, string literals, numeric literals, operators, comments, and other language-specific categories. Each token type is assigned a "scope" or category name, and the highlighting theme maps these categories to colors and styles. For most languages, lexical analysis alone is sufficient for accurate highlighting because the visual distinctions people need (keyword vs. identifier, string vs. code, comment vs. active code) correspond to lexical rather than syntactic distinctions.

However, lexer-based highlighting has limitations. Consider the expression `print` in Python — is it a built-in function or a user-defined variable? A lexer sees only an identifier; determining its role requires semantic analysis (understanding the scope and binding of names). Grammar-based highlighting systems, like the one used in Tree-sitter (developed by Max Brunsfeld at GitHub), parse the full AST of the source code and can make these distinctions. Tree-sitter uses incremental parsing, meaning it re-parses only the changed portions of a file when you type, making full AST-based highlighting practical even for large files. This approach has been adopted by Neovim, Zed, and other modern editors.

The TextMate grammar format, created by Allan Odgaard for the TextMate editor on macOS, became the de facto standard for syntax highlighting definitions. TextMate grammars use regular expressions organized into a hierarchical scope system — a pattern like `keyword.control.flow.python` describes a flow control keyword in Python. VS Code adopted TextMate grammars, and because VS Code's extension marketplace became the largest source of language support definitions, the TextMate format now defines highlighting for hundreds of languages. Libraries like Shiki and Prism.js bring these same grammars to the web, enabling server-side and client-side syntax highlighting in browsers.

Color theme design for code is a specialized discipline that balances aesthetics with functionality. Effective themes must provide sufficient contrast between token types while avoiding visual fatigue during long coding sessions. Dark themes like Monokai (created by Wimer Hazenberg in 2006) and Dracula (created by Zeno Rocha in 2013) became popular partly because they reduce eye strain in low-light environments and partly because bright colors against dark backgrounds create higher perceived contrast for syntax elements. The Solarized theme, designed by Ethan Schoonover, took a scientific approach by selecting colors based on CIELAB color space relationships to ensure consistent contrast ratios across all syntax categories.