Much to the amusement of @ElendilTheTall, I'm working on French macarons. I'm using the method that makes an Italian meringue, so I pour hot sugar syrup into the partially whipped egg whites.
The final result is supposed to look like this:
I'm not there yet :/. The recipes that I have consulted add powdered color to the unwhipped egg white and almond flour mixture (I don't have powdered color), or they add gel to the final mixture before folding. One of the recipes warns against that, that the liquid in the color will affect the consistency of the batter.
So why not add the color (and for that matter, any liquid flavoring you might be using) to the syrup? Just before it reaches soft ball stage (the stage at which it is added to the meringue)? The syrup has water in it anyway. It seems that you could even use ordinary liquid food coloring, three drops isn't going to affect the water measurement, kitchen scales are not accurate to fractions of a gram.
If, at the final stage, the color looks a bit too timid, I still can a drop of gel color (less than I would use otherwise) to the final mix.
Why would this be a bad idea?
My actual recipe is paywalled, but this method is close.
Best Answer
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?