Add albedo to material visualization

ray-tracing-core/src/color.rs

@@ -101,3 +101,9 @@ impl Mul<Color> for Float {
         Color::new(self * rhs.r, self * rhs.g, self * rhs.b)
     }
 }
+
+impl std::iter::Sum for Color {
+    fn sum<I: Iterator<Item = Self>>(iter: I) -> Self {
+        iter.reduce(|a, b| a + b).unwrap_or(Color::black())
+    }
+}