Use uniforms for color

shaders/fragment.glsl

@@ -1,6 +1,7 @@
 #version 330 core
-out vec4 color;
+in vec4 vertex_color;
+out vec4 final_color;
 void main()
 {
-    color = vec4(1.0f, 0.5f, 0.2f, 1.0f);
+    final_color = vertex_color;
 }