Hi Dunc. OK I used the red spheres!
this is a fine boulder puzzle, I enjoyed it very much, You left me with just enough items to get the job done, As usual Loof was on the sidelines taking a break and did nothing, Didn't need any of generators. Red herrings perhaps. Thanks for the challenge.
Well, I did use 2 of the red spheres and both of the yellow spheres! You provided enough stuff so I did not start any generators! This was an excellent challenge and I really enjoyed working it out my own way! Thanks Dunc!