It is a juniper, providing some difficulty for many beginner or casual bonsai gardeners. Most are purchased from the walmarts of the world, where they are usually advertised as 'indoor' plants, which they are not. They need winter dormancy outside, which requires cold without exposure to drying winds and frequent warmups/cooldowns. Luckily a dark shed or garage can do the trick.

When it is growing, as yours is, the new growth is a lighter green as you've noticed. There is some functionality in pulling off new growth, but that must be done conservatively. New growth has come at the expense of energy from the plant, and those new leaves are functioning better than older, established growth. It is most advisable when you want a tree to increase in size, or it is sick or weak, to let the new growth stay.

This tree is new to you, and young. I recommend letting it grow freely while you research juniper bonsai care. There are websites, such as bonsai4me and bonsai tool chest(and many others), and there are many good beginning bonsai books quickly found through a google search. Happy growing!

ez