fixed minor regression, cleaned up source tree

resources/shaders/simple_texture.vertex

@@ -6,6 +6,8 @@ layout(location = 0) out vec2 tex_coords;
 layout(location = 1) out vec4 out_color;
 
 void main() {
+    out_color = color;
+
     gl_Position = vec4(position, 0.0, 1.0);
     tex_coords = position;
 }