I find that macarons are a great canvas for painting with edible food colors, but it is important not to use water since the cookie can dissolve, instead mix the color with alcohol so that it doesn't soak. Fresh fruit is also a fun way of creating artistic decorations once dried, I've worked with pears in this case. Another fun way to work is with brush embroidery, it's well suited for weddings and baby showers, and the same applies for the painted macarons I'd say. I get a lot of requests for these custom made cookies but unfortunately they're only available for pick up in Stockholm, Sweden and not eligible for shipping.

Large macaron with painted rose
Rose meringues and purple pastry
Small pink rose macaron
Blue brush embroidery cookie
Handpainted macarons
Brush embroidery
Painted pears
Pear pastry
Dried painted pears