Using a standard modern red sequin on a pair of my slippers isn't something I was interested in, because when hit with light directly, you'll see flashes of orange. That's the same reason that MGM didn't use regular red sequins on their pairs. While the studio didn't have to resort to having a deep red sequin custom made, I did, as no modern sequin color was quite what I was looking for.

This custom made color is designed to reflect back more pink and violet tones instead of the orange color a regular red sequin would offer. The color was achieved using two samples that were sent to my manufacturer: the first was an embroidered sequin flower from the 1930's that had aged absolutely beautifully; the other sample sent included a number of 1930's wine red sequins that had been stored on the hank and hadn't aged as much as they would have if they had been sewn onto something. Using those samples, my manufacturer was able to create this custom color that is probably as close to the original slipper coloring as you can get. I have never believed MGM used a "dark" red sequin on the slippers - more likely, a "deep" red sequin was used. The deep red is achieved by adding more blue to the coloring.

The large glass jewels on the bows are a good indicator of what the original sequin color was close to. I've found vintage red jewels in 3 hues of red, which I call Light Siam, Siam, and Dark Siam. Light Siam reflects back orange when lit directly. Siam flashes back with red and pinks, whereas Dark Siam is a bit too dark. A photo of my glass jewel  coloring is included for reference.