If you're running iOS 7 (and if you've got a supported device, as noted in this TMO article), you'll get an icon to access new built-in filters when you're taking a picture.
After you choose whichever fanciness you wanna apply and take your shot, though, what if you decide you hate the filter you picked? It's actually pretty easy to strip it off after the fact. Just like when you edit images in iPhoto on your Mac, the changes are nondestructive; this means that you can always revert to the original picture if you want to, so here's how you'll do that. First, find your filtered photo within your Camera Roll and touch the Edit button.
In Edit mode, then, touch the Filters circle-bubble-icon-thingamajig.
That IS its official name, by the way.
When you've got the filters open, you can apply a different one to your image, or if you scroll all the way to the left, you'll see the "None" option.
Touch Apply, and your photo will revert to its non-filtered awesomeness. Or if your picture is anything like this one of my lamp, it'll simply remain an image of questionable value. At least it's now an image of questionable value that's in color.