Font colour of blog subscription form plugin

Hi
If you place the mail subscription form at the bottom of a blog post [blog_subscription_form], it comes in a white font colour which is illegible against the beige background. Since this is a feature of the Edda theme on wordpress.com, would it be feasible to change it?

My example: https://theleadersfairytales.com/2015/09/21/the-magic-urn-2/

Why is this necessary? I write to a not so blog savvy audience. Of the 40 or so people who have answered to my initial publicising email saying how they like it and how they are looking forward to reading future posts, only 5 have actually registered/followed on one of the channels offered.
Thanks for your help!
Bernhard