Function lumen_signal_set_color 

#[unsafe(no_mangle)]
pub unsafe extern "C" fn lumen_signal_set_color(
    name: *const c_char,
    rgba: *const u8,
) -> LumenStatus

Set a scalar signal to a 4-byte RGBA color (each channel in 0..=255). rgba must point to at least 4 bytes (R, G, B, A).

Pushes PropertyValue::Color (channels normalised to [0, 1] floats) through the typed-property bus.