one yucca that colors up a lot is color guard, becoming quite showy in winter.

lots of evergreen plants get purplish colors in winter many junipers, nandina, and arborvitae to name a few. it would be interesting if the color stays in the growing season. the very narrow leaves is the most interesting to me, usually plats get larger leaves in shade conditions.

if they are in deciduous woods they could be reaction to sudden sunny conditons.