diff --git a/crates/resolved-cli/tests/cli.rs b/crates/resolved-cli/tests/cli.rs
index b28aec4..9fb66d1 100644
--- a/crates/resolved-cli/tests/cli.rs
+++ b/crates/resolved-cli/tests/cli.rs
@@ -66,9 +66,10 @@ fn example_scene_on_gpu_and_cpu() {
     let [r, _, b] = gpu.get_pixel(960, 540).0;
     assert!(r > 500 && r > 2 * b, "{r} {b}");
     // Above the limb is empty space, which reads the 64 DN bias; below it, Earth's
-    // dayside.
+    // dayside, lit and blue.
     assert_eq!(gpu.get_pixel(0, 0).0, [64; 3]);
-    assert!(gpu.get_pixel(0, 1079).0.iter().all(|&d| d > 300));
+    let [r, g, b] = gpu.get_pixel(0, 1079).0;
+    assert!(r > 64 && g > r && b > g, "{r} {g} {b}");
     let differing = gpu
         .pixels()
         .zip(cpu.pixels())
diff --git a/crates/resolved/src/bodies.rs b/crates/resolved/src/bodies.rs
index 0e934b7..4c6be67 100644
--- a/crates/resolved/src/bodies.rs
+++ b/crates/resolved/src/bodies.rs
@@ -24,12 +24,45 @@ pub struct Appearance {
 }
 
 impl Default for Appearance {
-    /// Flat spectra: 0.3 for Earth (its Bond albedo) and 0.12 for the Moon (its
-    /// average visible normal albedo).
+    /// A blue-tilted stand-in for Earth until albedo maps arrive (M2), and a flat 0.12
+    /// for the Moon (its average visible normal albedo).
+    ///
+    /// Earth's spectrum is shaped like cloud-free ocean seen through the atmosphere,
+    /// where scattered sunlight makes the blue end several times brighter than the
+    /// red: 0.32 at 350 nm, 0.21 at 500 nm, 0.07 at 650-700 nm, then back up to 0.20
+    /// in the near infrared, where clouds and land reflect strongly. In the example
+    /// camera that is an albedo of 0.09, 0.15 and 0.26 in red, green and blue. Earth
+    /// gets its color through the same per-channel folding as everything else; its
+    /// overall brightness is lower than the real, partly cloudy Earth's (about 0.3).
     fn default() -> Self {
+        let nm = [
+            350.0, 450.0, 500.0, 550.0, 600.0, 650.0, 700.0, 750.0, 850.0, 2800.0,
+        ];
+        let earth = [0.32, 0.29, 0.21, 0.13, 0.09, 0.07, 0.07, 0.10, 0.20, 0.20];
         Self {
-            earth_albedo: Spectrum::constant(0.3),
+            earth_albedo: Spectrum::sampled(nm.map(|x| x * 1e-9).to_vec(), earth.to_vec())
+                .expect("fixed samples"),
             moon_albedo: Spectrum::constant(0.12),
         }
     }
 }
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use crate::camera::CameraConfig;
+    use crate::radiometry::Radiometry;
+
+    #[test]
+    fn default_earth_is_blue_in_the_example_camera() {
+        let r = Radiometry::new(&CameraConfig::example());
+        let [red, green, blue] = r.effective_albedo(&Appearance::default().earth_albedo)[..] else {
+            panic!("three channels")
+        };
+        // Measured: red 0.086, green 0.152, blue 0.258.
+        assert!(
+            blue > green && green > red && blue > 2.0 * red,
+            "{red} {green} {blue}"
+        );
+    }
+}
diff --git a/crates/resolved/tests/sensor.rs b/crates/resolved/tests/sensor.rs
index be45e2a..e0fe6eb 100644
--- a/crates/resolved/tests/sensor.rs
+++ b/crates/resolved/tests/sensor.rs
@@ -10,7 +10,7 @@ use resolved::gpu::targets::FrameTargets;
 use resolved::gpu::GpuContext;
 use resolved::nalgebra::{UnitQuaternion, Vector2, Vector3};
 use resolved::radiometry::{Radiometry, AU};
-use resolved::{CameraConfig, Pose, Scene};
+use resolved::{CameraConfig, Pose, Scene, Spectrum};
 
 /// Runs the sensor pass over `radiance` (example camera, rows from the top) and
 /// returns the DN image.
@@ -143,7 +143,12 @@ fn sunlit_earth_through_the_whole_chain() {
         Vector3::z(),
     )
     .unwrap();
-    let body_radiometry = BodyRadiometry::new(&radiometry, &Appearance::default()).unwrap();
+    // A flat gray 0.3 Earth, as in docs/optics.md's worked example.
+    let gray = Appearance {
+        earth_albedo: Spectrum::constant(0.3),
+        ..Appearance::default()
+    };
+    let body_radiometry = BodyRadiometry::new(&radiometry, &gray).unwrap();
     let bodies = BodiesUniforms::new(
         &scene,
         &camera,
diff --git a/docs/optics.md b/docs/optics.md
index 691fb0e..c4574c3 100644
--- a/docs/optics.md
+++ b/docs/optics.md
@@ -418,8 +418,16 @@ disk, which is the feature horizon-based navigation measures.
 
 ### Shading
 
-Earth and the Moon are Lambertian, with one albedo each, set by
-`Appearance`: 0.3 for Earth and 0.12 for the Moon, flat across wavelength.
+Earth and the Moon are Lambertian, each with one reflectance spectrum over
+the whole body, set by `Appearance`. The Moon's is a flat 0.12. Earth's
+default is a stand-in shaped like cloud-free ocean seen from space: about
+0.3 in the blue falling to 0.07 in the red, then back up in the near
+infrared. Most of that blue is sunlight scattered by the atmosphere above
+the ocean, the same scattering that makes the sky blue; the ocean itself is
+dark. In the example camera it gives channel albedos of 0.09, 0.15 and 0.26
+(red, green, blue), so Earth renders blue. Its overall brightness is below
+the real Earth's average of about 0.3, which includes bright clouds.
+
 Each point's radiance is rho cos(i) S_k / (pi d^2), with i the angle between
 the surface normal and the Sun. The night side has i past 90 degrees and is
 black. The Sun's distance d is taken from each body's center, since the