To make things easy on myself, I bought pre-made sugar cookie dough from Fresh Direct (it is so good) and Royal Icing base from NY Cake and Baking Distributor.
Here is the process step-by-step:
First, I gave each cookie a coat of white royal icing, which I thinned to make a "picture" or "flow" icing. It spreads really easily and dries as a smooth, perfect finish.
Next, I piped white icing at the neck and seams:
Third, I piped a light green stripe on the body.
Last, I piped the blue strips and this is the final result (a mere four hours later):
These were a ton of work, but they turned out so great. I wish you could see the colors better in the pictures - I used just a little dye to make light baby colors and my flash washed it out a bit. Anyway, they were a big hit at the shower and I'll definitely make them again.