In my lot, I have used the terrain airbrush tool to change the entire lot to a different grass color. I don't want it to be this grass color anymore, as I want it to match the terrain color of the neighborhood. How do I revert the terrain color of this particular lot back to the original color of the grass?

You can just use the terrain paint tool and hold the ctrl key to actually delete terrain paint. Using the bigger brush will obviously go faster.

Oh my gosh thank you! Duh...I can't believe I didn't know this before now...do you by any chance know how to level the terrain for an entire neighborhood?

"raises hand": I know that answer!
In order to level any terrain in a neighborhood (presuming you don't have (I think) BV), you can take an empty house and move it around the neighborhood to level each bit of terrain by placing it all around the streets that you want to level.
This is time consuming and tedious-but short of creating your own terrain in SC4, it's the only other way to do it.
The trick is to make sure each side is level, and that takes some doing. I've done it many times before, and messed up a terrain to the point of absurdity. In that case, I do it all over again. You should use as large a lot as you have, to do it quicker.
Hope this makes sense.

It does make sense, thanks! But my problem ended up resolving itself...I eventually got frustrated and deleted the 3 lots I had been trying to level with each other, which caused all of the land to automatically level for some reason...lucky me!