Answer: Some perennials, such as iris, can undego blossom color change as a response to stress. Many hollyhock plants are biennial -- that is, they live only two years, blooming and dying after the second year. I suspect your pale pink did not overwinter and that the red was a first year seedling that hitched a ride in with the pale pink hollyhock. Many hollyhocks are grown from seeds sold as a color mix, so this is plausible. If you want to keep pale pink hollyhocks as part of your color scheme, you'll need to plant new ones every year to guarantee that they bloom consistently, or choose a variety that produces pink-bloomed offspring from dropped seed.
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