diff --git a/main.c b/main.c
index ffc6718..e1dac5e 100644
--- a/main.c
+++ b/main.c
@@ -1,3 +1,4 @@
+#include <math.h>
 #include <stdbool.h>
 #include <stdio.h>
 
@@ -6,20 +7,26 @@
 #include "ray.h"
 #include "vec3.h"
 
-bool hit_sphere(point3 center, double radius, ray r) {
+double hit_sphere(point3 center, double radius, ray r) {
   vec3 oc = point3_sub(r.origin, center);
   double a = vec3_length2(r.direction);
   double b = 2 * vec3_dot(oc, r.direction);
   double c = vec3_length2(oc) - radius * radius;
   double discriminant = b * b - 4 * a * c;
-  return discriminant > 0;
+  if (discriminant < 0)
+    return -1.0;
+  else
+    return (-b - sqrt(discriminant)) / (2.0 * a);
 }
 
 color ray_color(ray r) {
-  if (hit_sphere((point3){0, 0, -1}, 0.5, r))
-    return (color){1, 0, 0};
+  double t = hit_sphere((point3){0, 0, -1}, 0.5, r);
+  if (t > 0.0) {
+    vec3 n = vec3_normalize(point3_sub(ray_at(r, t), (point3){0, 0, -1}));
+    return (color){0.5 * (n.x + 1), 0.5 * (n.y + 1), 0.5 * (n.z + 1)};
+  }
   vec3 unit_direction = vec3_normalize(r.direction);
-  double t = 0.5 * (unit_direction.y + 1.0);
+  t = 0.5 * (unit_direction.y + 1.0);
   color gradient1 = {1.0, 1.0, 1.0};
   color gradient2 = {0.5, 0.7, 1.0};
   return color_lerp(gradient1, gradient2, t);