"Dark Blue" was adopted as the Society color.

The evidence

• “From the records of the Society, it appears that on the 30th of October, 1849, " Dark Blue " was adopted as the Society color.”

  1879-history-of-rock-county/15-rock-county-ch09-beloit.md, PDF p. 617 / book p. 621

  Butterfield, C. W., et al. The History of Rock County, Wisconsin: its early settlement, growth, development, resources, etc. Chicago: Western Historical Company, 1879. Cornell University Library via the Internet Archive, archive.org/details/cu31924028871585.

  Grade A: Found on a page of one of our sources