Junipers normally change color when outdoors for the winter, but I don't think the color change you got is particularly healthy. Just leave it be and see if it greens up in spring. Some faint hope.
Practice trees - my time is too valuable to waste it on ''practice'' trees. Every tree I have, I take seriously, and try to create the best bonsai I can out of it. I don't let myself get ''sloppy'' or take ''half measures'' because I don't care if it lives or dies. Treating each tree, no matter how cheap, as a tree to take seriously, helps you to learn proper technique. Once you have technique learned to the point where it is almost reflex, you can then begin to really creative. But you need to get the techniques down, including the horticulture. So take every seedling you go through the trouble of digging up or planting as seriously as your most expensive tree and you will find that you will learn more quickly.
My plant collection has seen enough carnage, I need to seriously keep on top of the horticulture. Though I do try to have fun, and I do try to keep it affordable. I start a fair number of trees from seed, so I know most won't ''make the final cut'' in the future, but I seriously try to get the best I can out of them. I only have 4 or 5 trees that I paid more than $100 for, most of my stock is either self collected, or cheap stuff found at nurseries or whatever.
I do have some trees, that were ''practice trees'' that I suddenly realized they survived much longer than I expected. As a result, that branch that I said to myself was too straight, and should be wired some 8 years ago is now too thick, woody and brittle to bend now. This is what happens when you don't take that little ''practice tree'' seriously when you first start with it. If I had corrected the ''too straight'' branch on that satsuki some 8 years ago when I first noticed the problem, I would not be kicking myself today about having an awkward branch on a 12 year old tree that otherwise has started to look really interesting.
So take all your tree seriously, knowing many will not make the grade, but some will and often not the one's you initially planned on making the grade.