In this answer is explained how to create an object which looks like a nucleus.
However, I have a problem when merging multiples spheres into one object. Exactly what I do is the following
1) I created a parent object with many spheres.
2) Then I do Object -> Apply -> Make duplicates real. This will give me all spheres, which are as before colored in red and blue.
3) I select all these spheres and Object-> Join (Ctrl-J). This gives me a single object that I would like to further use as a base object for other geometry.
But after step three all spheres become of the same color.
The question is how to preserve colors of individual spheres when Joining them into a single object?
Thanks in advance. (I was using blender 2.80)