diff --git a/zigrtiow/src/main.zig b/zigrtiow/src/main.zig
index ae6ace6..abcae73 100644
--- a/zigrtiow/src/main.zig
+++ b/zigrtiow/src/main.zig
@@ -10,21 +10,27 @@ const info = std.log.info;
 const write_color = color.write_color;
 const Ray = ray.Ray;
 
-fn hit_sphere(center: Point3, radius: f32, r: Ray) bool {
+fn hit_sphere(center: Point3, radius: f32, r: Ray) f32 {
     const oc = r.origin().sub(center);
     const a = Vec3.dot(r.direction(), r.direction());
     const b = Vec3.dot(oc, r.direction()) * 2;
     const c = Vec3.dot(oc, oc) - radius * radius;
     const discriminant = b * b - 4 * a * c;
-    return discriminant > 0;
+    return if (discriminant < 0) -1 else (-b - @sqrt(discriminant)) / (2 * a);
 }
 
 fn ray_color(r: Ray) Color {
-    if (hit_sphere(Point3.init(0, 0, -1), 0.5, r)) {
-        return Color.init(1, 0, 0);
+    var t = hit_sphere(Point3.init(0, 0, -1), 0.5, r);
+    if (t > 0) {
+        const n = r.at(t).sub(Vec3.init(0, 0, -1)).unit();
+        return Color.init(
+            n.x() + 1,
+            n.y() + 1,
+            n.z() + 1,
+        ).scale(0.5);
     }
     var unit_direction = r.direction().unit();
-    var t = 0.5 * (unit_direction.y() + 1);
+    t = 0.5 * (unit_direction.y() + 1);
     return Color.init(1, 1, 1).scale(1 - t).add(Color.init(0.5, 0.7, 1.0).scale(t));
 }