Black leaves on a evergreen

Ok, so I have this little bonsai I bought from wal-mart (yeah not the best place to get one but it was cheap and I'm just learning), I belive it is a juniper. I had always been worried about the pot it was in because it didn't seam to have any way to drain. Today I was looking at the little tree and noticed that some of the leaves had turned almost black. Fearing root rot, I repoted the little plant, and relized that the soil was not as wet as I had feared. Now I'm wondering if I diagnosed the tree properly. The leaves do not seam to indicate that the tree was tunderwatered either, they did not urn brown or seam dry. The roots on the surface of the soil also looked dark almost black aswell , ones deeper in the pot were a lighter red-brown.
Anyway I'm afraid I don't have a digital camera to take a picture of the tree.

On another topic, I've been looking for correct soil to use for bonsai, as I don't have a bonsai supply store I've been trying to find something that would work. At the gardening center I chose 'Miracle-Gro® Cactus, Palm and Citrus Soil' for the ingrediants (sphagnum peat moss, sand, and more) and the 'well draining' advertisement, and that is what I potted this little tree into (I have no idea what it was in). Since buying that I have wondered about buying a 'tree and shrub' mix for outside tree's from Lowes wonding if that would work better for bonsai. Any tips on that?

I killed my first Juniper 20 years ago. Welcome to the club.
Where are you keeping it? It should have been outside in full sun.
You do not repot Junipers in June. They are repotted in March or April.
You can learn to make your own bonsai soil. Meanwhile, the cactus soil will do, but add about 1/3 aquarium gravel or crushed granite chicken grit.
For now, keep the plant in the shade until it show signs of recovery. I trust you now have it in a pot with adequate drainage. Do not water until the soil at the bottom of the pot is almost completely dry.
Iris

It was in my house on my computer desk most of the time, though I took it out nearly every day while I was on a walk. Its outside now, thought my covered front porch would do it good to help it recover.
Yeah, I didn't think about the timing for the repot, but I was really worried about its current pot damaging it more than a quick repot, I did my best not to damage the root-ball in any way.
Thanks for the tip on the graval I'll pick some up ASAP. I looked into making my own soil some too when I bought the cactus mix. I have a book 'Successful Bonsai by David Squire' That outlined common ingrediants and proportions for the soil. However, when I went to go buy it, the store only sold things like Lava Rock, bark and grit by the ton.... and I have absolutly No way to deal with a ton of EACH the stuff.
As for the pot, is probably a lot better match for a bonsai, The other pot was square and fairly deep with no drainage at all (found that out after pulling the bonsai out of it). Now its in a shallower rectangle (that honestly looks better with the tree) with two drainage holes (I wired in a screen over them to keep the soil from being lost).

I hope it doesn't die. But it won't be a big loss if it does, the more I learn the more I realize why it was at walmart for 10$ lol. But its been good company while I wait for the tree's in my garden to grow. (Yes, I did take advice last time to let the tree's grow in the yard for a while! ^^)

Thank you for the help. I'll try to baby this one back to health. If all else fails; I have a couple of Birch tree's to look forward to soon. I found them growing in the rosebush at this house, someone neglected to remove them... like YEARS ago. So I'm waiting until late fall when all the foliage dies off to move them out of the bush and begin training.

You CANNOT keep any bonsai on your computer desk. It must be outdoors all the time.
Sorry, American birch are not recommended for bonsai.
If you want to know what to collect in Pennsylvania, contact Jim Doyle at Nature's Way Nursery. But beginners are advised not to start with collected trees. Practice on some nursery trees first.
Iris