In the 1850s, the color yellow could be created either with chemical dyes or with dozens of different vegetal dyes. The four natural dyes most often found in dyer’s manuals of the time were quercitron bark, weld, fustic, and turmeric. Of those, quercitron was the most common due to its combination of strength and economy. Weld, a popular yellow dyestuff for centuries, was still used a great deal. Turmeric would have been the most expensive option, but is definitely not the culprit here: its hallmark is a warmer, golden color. The last option, fustic (both ‘old’ and ‘young’), does not yield so vivid a shade as this, nor one so colorfast.
Additional reading: Hansen, Heather Nicole. The Quest for Quercitron: Revealing the Story of a Forgotten Dye. Master’s Thesis, Winter 2011. University of Delaware.