Try using Lock Alpha layers. On the box in the bottom right, there should be a list of different layers. Take off the 2nd that says 'Remove to Color' by clicking the black dot next to the name. (You can turn it back on by clicking it again.)
Next, scroll down the list until you see 'Color bunny (Lock Alpha)' and click on it the box (not the dot). Check the box at the top of the layers box that says 'Lock Alpha.' Set the pencil or pen to whatever you want and color in that layer. it will stay in the lines.
To change the colors of the shadows/ears/highlights/etc, click that layer's box and use Lock Alpha. (It will stay in Lock Alpha unless you turn it off)
You can remove layers you don't want by clicking their dots. This editable comes with clothes and backgrounds and fun stuff like that, so to add them, you find the box labeled with whatever you want to add and click the dot to turn it on. You may have to add your own layers to color them in. (Use the + button) Click the box UNDERNEATH the one with your item, then add a new layer. Lock Alpha won't work on these, though, and you'll have to color it in manually, but it will not cover the item's lines.
This help?
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