fixed!!

shaders/triangle.frag

@@ -5,5 +5,5 @@ layout(location = 0) in vec3 pos;
 layout(location = 0) out vec4 f_color;
 
 void main() {
-    f_color = vec4(pos, 1.0);
+    f_color = vec4(.3, .1, .8, 1.0);
 }