[Bug] Diff highlight colors (added/removed text) broken in v0.0.421 — unreadable on dark terminals

[indeherb]

Describe the bug

Bug Description

Since the latest update (v0.0.421), the color scheme for highlighted added/removed text in file diffs is broken. The background colors are very saturated bright red and bright green, with white foreground text — which has near-zero
contrast against the background and is visually painful on dark terminal themes (e.g. WezTerm with dark background).

Expected behavior

Subtle, readable diff highlighting — muted green/red tones with sufficient contrast between foreground and background text.

Actual behavior

• Added lines: bright/saturated green background + white foreground → text barely readable
• Removed lines: bright/saturated red background + white foreground → text barely readable
• On dark terminal backgrounds the contrast is especially poor and eye-straining

Environment

• Copilot CLI version: 0.0.421
• Terminal: WezTerm (dark background theme)
• OS: Windows

Request

Please revert to the previous, more subtle diff color scheme, or make it configurable so users can adapt it to their terminal theme.

Screenshot

Affected version

GitHub Copilot CLI 0.0.421

Steps to reproduce the behavior

1. Ask Copilot CLI to make edits to an existing file (e.g. "update this function")
2. Copilot shows a diff preview with highlighted added/removed lines
3. Observe that the highlighted text is unreadable due to poor color contrast

Expected behavior

Diff highlights should be clearly readable — as they were before v0.0.421. Sufficient contrast between background and foreground so changes are legible at a glance.

Additional context

Worked fine in previous versions. Color scheme regressed in v0.0.421 — new saturated red/green backgrounds with white text make diffs hard to read, especially on dark terminal themes like WezTerm.