I assume this is for learning purposes and that's why you don't use wrangle
in your Vopnet you already have Cd bound, but since it's not connected it's not gonna be exported and therefore treats it as read only
- so jump into your VOPnet and delete geometryvopoutput1 and geometryvopglobal1
- set Bindings to Export on snippet1 to: * or at least Cd
- also you can return your vexpression to be using color as you have it connected inside :