Regression: fenced code blocks render with white text on light backgrounds (v1.2.24)

[KimDaehyeon6873]

Summary

Fenced code blocks render with white/near-white foreground text on light terminal backgrounds, making them invisible. This is a regression of previously fixed issues #16508 and #16731.

Environment

• OpenCode version: 1.2.24
• OS: macOS (darwin, arm64)
• Terminal: iTerm2 3.6.9
• Terminal theme: Poimandres Light (light background #fefeff)
• OpenCode theme: opencode (with theme_mode: "light")
• COLORTERM: truecolor
• TERM: xterm-256color

Reproduction

1. Use a terminal with a light background color scheme
2. Run OpenCode with any theme in light mode (tested: opencode, system, catppuccin, and others — all exhibit the issue)
3. Ask the AI to provide a response containing fenced code blocks (untagged, text tag, or unknown language), flow diagrams, or commit lists
4. Observe: fenced code block text is white/near-white, invisible against the light background

What is visible

• Inline code (single backticks)
• Known language-tagged code blocks (e.g., python)
• Headings, bold text, other markdown elements
• Dark mode rendering (all text visible)

What is invisible

• Untagged fenced code blocks
• Fenced code blocks with text or unknown language tags
• ASCII diagrams, commit lists, and other preformatted content inside fenced blocks

Workaround

Disabling the experimental markdown renderer resolves the issue:

export OPENCODE_EXPERIMENTAL_MARKDOWN=0

Root cause (from #16508 analysis)

The experimental markdown renderer's code block rendering path falls back to a hardcoded white foreground when syntax highlighting is unavailable for the block, instead of inheriting from the active theme's text/code-block color tokens.

This was previously fixed for #16508 and #16731 (reported on v1.2.20–1.2.21), but has regressed in v1.2.24.

Related issues

• Light themes: fenced code blocks can ignore theme colors and render with hardcoded white foreground #16508 — Light themes: fenced code blocks can ignore theme colors and render with hardcoded white foreground
• Code blocks render with white text on light backgrounds #16731 — Code blocks render with white text on light backgrounds

[github-actions]

This issue might be a duplicate of existing issues. Please check:

• Code output unreadable in light mode #16470: Same symptom — code blocks rendering with white/invisible text on light backgrounds, same workaround (OPENCODE_EXPERIMENTAL_MARKDOWN=0), same root cause in the experimental markdown renderer

If this is the same issue, please consider adding your details there instead so fixes can be tracked in one place.

[KimDaehyeon6873]

Closing as duplicate of #16470 — same root cause (experimental markdown renderer hardcodes white foreground for fenced code blocks in light mode). Added reproduction details there.