The author remixed this model.
My wife wanted some contrast adding to the shell of the turtle, so I remixed the original to allow me to use my MMU2S to add a second colour to the shell ‘grid’. The .stl files have been split to create separate files for each model piece.
The same effect can be created using a single colour printer (i.e. without an MMU2S) by setting a colour change from layer 3 (0.6mm assuming a 0.2mm layer height). In this case, just use the original model files from Simple3D.