I also use Toba's recipe and I add some white airbrush color to it, works great. I have a pic of one of my recent cookies in my album. To answer your question, you just need thicker for the outline. I don't want to bother with two bowls, so I mix mine as called for in the recipe but I don't add all the water. I measure it out, add it slowly, until I get the thick (cold honey) consistency which works best for me and I go ahead and outline all my cookies. It gets a chance to set up a bit while I add more water and get the consistency I like. Honestly, you won't stick to the exact amount of water called for in the recipe each time because powdered sugar is a bit tricky, sometimes it has more corn starch in it than others so that's why you won't always use the same amount of water from one time to the next. You want it thin enough, so when you drop a drop on some waxed paper or something that it flattens out but still "coats" the spot, does that make sense? If you were to drop a bit of your icing onto the countertop, you don't want it to run like a liquid...You want a little staying power. More of a room temp honey type flow.
I use royal for details once the cookie icing is dry. It adheres well and gets soft to bite after sitting on the glace. In other words, it doesn't crumble in your lap when you bite into it like straight royal iced and decorated cookies do!
I hope that helps.