I love macarons because they're so pretty and they don't need a lot for that. A plain macaron looks fine the way it is, but there are ways to make it prettier.
* Top your macarons with a main ingredient in your macaron. If you're making pistachio macarons, top them with crushed pistachios; black sesame macarons topped with black sesame seeds; tea macarons topped with tea leaves; sprinkles etc. You just have to make sure that what you're topping the macarons with is dry. You don't want to add excess liquid to the macaron batter, which would affect the macaron during the baking process.
* After filling your macarons, you can roll them in a main ingredient for the macaron, similar to the topping.
*Add swirls of colour in your macaron by painting the food colouring down the pastry bag before you fill it with the batter. I've only done this with one colour just because it looks better in my opinion. It just gets too crazy if you have a multicoloured macaron. You end up with a cool marble effect.
* You can tint your macaron batter different colours as well. I tried this, but it didn't work for me. You have to make sure that your batter is mixed enough, and then split the batter to colour it. You could risk overmixing your batter, which I ended up doing. I haven't tried this more than once.
* You can paint your macarons with food colouring. I think it works best with liquid food colouring mixed with a little water. Use whatever colour you want and paint your macarons after baking with a pastry brush. You'll have to practice a little to get the hang of it and to figure out what looks good on the macaron.
The possibilities are endless! But remember, you don't have to do any of this because macarons are already perfect the way they are :)