(require pict3d)
(combine
(with-color (rgba "red")
(sphere (pos 1 0 0) 1/10) )
(with-color (rgba "blue")
(sphere (pos 0 1 1) 1/10) )
(for/list ( [ t (in-range 1/10 1 1/10) ] )
(define v (pos-between (pos 1 0 0) (pos 0 1 1) t) )
(sphere v 1/20) ) )