What does Redcast mean?

A style of denim that is known to have a redish tint.

Heddels explains Redcast

Redcast denim, so named because of its slight red tint, is denim that has only been dyed with indigo. Unworn redcast denim will have an almost purplish tint to it. After the jeans have been worn for some time, the denim will fade to a clean, brilliant blue color.

Additional Resources

Here is an example of redcast denim:

Lee Jeans 120 collection denim with red cast finish:

Source: denimology.com