Sweaters?

[wellington]

She has a carpeted room

You really need to read the caresheet and get her set up properly. Carpet is not meant for tortoises and the fibers can cause impactions.
She needs proper tortoise substrate, heat, UV, water, hydration, temps, all that is meant for the species you have.
Changes are needed ASAP.

 

[Alex and the Redfoot]

Wouldn't darker skin maximize the D3 synthesis as darker colors attract heat/sun more? Or, is what you are saying, the lighter skin would let it in easier?
Thanks for the post.

There is an old article on the topic (biochemistry and physiology, probably, have advanced since then): http://www.uvguide.co.uk/skintests.htm
It's not about tortoises, but gives general idea why pale skin can be beneficial for UV absorbtion.

Yet, markw84's idea is interesting. I wish we could see some recent research on this topic.