Change was also due to the new synthetic dyes featuring..

.. new intense hues of magenta, purples, blues, and greens.  The early 1870’s with a sudden interest by the public in science led to many new inventions at the time.

(Photo: extant dress estimated to be 1873 in the new synthetic purple previously reserved for royalty as purple was expensive and difficult to process using natural dyes (see April posts on the evolution of dyes in this mid-Victorian era)