Color in 3D printing

[LambdaFF]

Good evening,
I would like to know at what point you integrate the colour parameter in your designs destined to be printed in printers with more than one head ?
Do you make separate STLs ? Or is it something done at the slicing stage ?
Thank you for your experience

[Geoff]

if you want to dual extrude at the same time, you need alternate STL files, its basically one print head per STL file. Alot of machines also allow you to pause and change filament, which isnt as clean but it does work if you are doing multicolours in one STL file.