Function render_to_png_with_background 

pub fn render_to_png_with_background(
    chartml: &ChartML,
    yaml: &str,
    width: u32,
    height: u32,
    density: u32,
    background: [u8; 3],
) -> Result<Vec<u8>, RenderError>

Render a ChartML YAML spec to PNG bytes (synchronous) with an explicit canvas background color.

Identical to render_to_png except the pixmap is filled with background instead of white. Use this when the PNG will be placed on a non-white surface (e.g. a dark-mode email card) — the theme set on chartml should use matching colors or chart text will be illegible.

Arguments

• chartml — configured ChartML instance with renderers registered
• yaml — ChartML YAML specification string
• width — chart width in CSS pixels
• height — chart height in CSS pixels
• density — DPI (72 = 1x, 144 = 2x for PDF)
• background — canvas fill color as [r, g, b]