Macarons...Why not color the syrup?
I wouldn't do it. One of the hardest things about macarons is to stop just when everything is perfectly mixed together, not a stroke earlier or later. 

When you have a small blob of gel color just before you start the macaronage, you will know when everything is mixed well: at the point at which your color is dispersed evenly, you are ready. It is a good indicator, helping you make better macarons. 

If you color your syrup (and thus your meringue) evenly, you will lose the important indicator function. I guess you could pull it off once you are a macaron master who can sense the moment to stop, but especially at the beginning, why give the benefits up?