For a two color print, you will need at least two STL files to convey each of the colors
Download the STLs for the different colors
For this part it was named solid and hollow for the different colors
Under the Files tab in 3DPrinterOS, you can make a new project (if you want) and upload those two files
Next to one of the files, click Layout
If your object is out of the printer box then click On bed to get it inside the print volume.
First, make sure you have selected the correct printer under the printers tab. Either the Ultimaker S3 or S5 depending on which one you want to use.
If you don’t have it under My Printers, just search the All Printers box
Next, under the Add File tab, you want to select the file for your other color.
Select your project, then the file of the other color and click Add
Now the file will be under the one you have now. You will then want to click On Bed.
On the right, the different files will be listed. Click on one and select the eye symbol to hide it
From there, click on the visible part in the middle of the bed.
Then select Extruder and select which extruder you will want to use.
If it is the second extruder, then click on it and hit Apply.
Whatever color is loaded in that extruder is what that color will be.
Make the other part visible again
If your two parts are not lining up exactly with each other, use the Center button on each of them. Your parts should have been designed to have the same origin.
Then click Slice & Toolpath Preview. It may take longer because it is more complex to slice.
From here you can click Slice and choose the profile for the printer you want. I am going to choose Leia because I want a green and white frog.
Then click Print and select the printer you want to send it to and click Print again
This will not go into the details about making the CAD, but the most important thing is that you make everything you want into different colors into different bodies
To make different bodies, when you extrude, select New Body under Operation
In this nameplate file, I have 17 different bodies, one for each of the letters, the outside plate and each of the middle of the letters
For every body that you want of one color, make those visible and the bodies of the other color invisible by clicking on the eye symbol next to the body name
Now right click on the top component and select save as mesh
Change Format to STL Binary and click Ok
Then save as an STL file and do the same thing with the other bodies