Dynamo primer: how to make exercise 4.5.4

I’ve start learning Dynamo and I’m following the exercises from dynamoprimer.com.

Can someone help me with exercise 4.5.4: http://dynamoprimer.com/04_The-Building-Blocks-of-Programs/4-5_color.html? I can make spheres (instead of cube), I can make a color range, but how do you make the progress in diameter and how do you make the link between that progress and the colors?

I’ve added the file I’ve so far. kubussen in kleuren