small refactor

shader/instancing_vertex.glsl

@@ -1,10 +1,14 @@
 #version 330
 
-in vec3 vertexPosition;
-in mat4 instanceTransform;
+layout(location=0) in vec3 vertexPosition;
+layout(location=1) in mat4 instanceTransform;
+layout(location=5) in vec4 instanceColor;
 
 uniform mat4 mvp;
 
+out vec4 fragColor;
+
 void main() {
+     fragColor = instanceColor;
     gl_Position = mvp * instanceTransform * vec4(vertexPosition, 1.0);
-}
+}