Hi,
im new to bonsai and i didnt find much Information about Thyme Bonsai Winter care.
I left it outside the winter covered in a greenhouse. Now the the plant changed from green to a brown, did i kill the plant? Or is it normal that a thyme changes colour in the winter ? 
If it did hurt the tree, is there a trick to help the Tree recover?
Is that thyme or rosemary? Regardless it doesn’t look to happy better pictures would help to assess. Don’t overwater and balance water and oxygen.
Your name tag doesnt say where you are or your temps… Should still be alive…
The three flavors of prostrate thyme I have in the ground here survive, mostly die back every winter. They green up and fill in their space quickly. Winters go down to -10 some years. I keep small pots of Elfin thyme for bonsai companion plants. The several pots of weaping Elfin thyme I grew last summer went into an unheated outbuilding with south facing windows. They were still green and ready to go this week!
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(Note: there are several small conifer and decideous seedlings/ cuttings mixed in, moss too…)
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I tried several large trunked rosemary for bonsai. They are readily available . Froze and died…
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Post the outcome!
Bonsai On!
Thanks so much the replies. I live in southern Germany. The lowest temperatures were -7 °C, I think, when the bonsai was outside. Now I keep the Bonsai at low temperatures in my stairwell to recover. The temperature should be around 15 Celsius in there, and when it gets warmer again, I take it outside again
The comments gave me hope that it isn’t dead. I hope a can bring it back to thrive 
Are the green bits dry crunchy, and the smaller branches brittle?
K
Yes, some of the old Green bits are a bit flexible, but i think they get more crunchy over time
