Here's another early fountain pen with an Esterbrook "Colorado" nib in an ad from the
American Stationer, but here it's called a bronze nib. The Diamond Point Pen Co. started off with ads for fountain pens with Aluminum nibs, but then they progressed to pens with "Colorado Bronze" nibs, probably supplied by Esterbrook.
Since they had Esterbrook supply the bronze nibs, they probably got their Aluminum nibs from another supplier as well, someone such as A. L. Salomon.
But then they finally progressed to 14kt gold nibs as well. They started off making cheap novelty fountain pens, but they ended up making good-quality, second-tier pens, especially their RHR pens in the 1920s.
Here are some of their later pens in an image from Bruce Marshall's website,
Fountain Pen Resources. I love the flared, trumpet-shape of the section, and the two little side kerfs on the broad, flat-bottomed feed.
George Kovalenko.