Feature | Set the background color of the native window body

[AnnaSasDev]

Impact

Medium

Problem / Motivation

No dedicated native-window background color API in builder/runtime; transparency is available but not color control.

Current behavior

Relevant primitives exist in the files listed above, but this backlog item does not have a complete, explicit InfiniFrame contract with dedicated coverage.

Expected behavior

Define explicit API/behavior for this migration item, implement in managed + native layers where needed, and add focused tests/documentation.

Proposed solution

Implement this incrementally:

1. Define/adjust the managed public API in InfiniFrame.Shared.
2. Wire implementation in InfiniFrame and InfiniFrame.Native where required.
3. Add focused tests (tests/InfiniFrameTests*) and docs updates (docs/docs/guides/*, docs/docs/migration/*).

Alternatives considered

• Keep as unsupported and document migration limitation.
• Provide a workaround-only approach without first-class API.

Use case

Applications migrating from Photino expect this behavior and currently need custom handling for "Set the background color of the native window body".

Technical proposal

Scope implementation to: core managed runtime (src/InfiniFrame/*, src/InfiniFrame.Shared/*, src/InfiniFrame.Js/*). Keep behavior deterministic across Windows/Linux/macOS and document platform-specific limitations explicitly.

Additional context

Photino reference: tryphotino/photino.NET#239

Checklist

• I searched existing issues
• This is not a support question