goldfish cutters are handmade with built-in eye cutouts; very intricate and precise. I have found that carrots are the optimal substrate for this cutter: they are the desired color, and they are stiff enough to hold up well to display the lovely curved shape. If you cooked sweet potato only until firm, you might get a nice result (but I like sweet potato much softer).
I also quick-sauteed horenso (spinach) in garlic and shoyu and topped with sesame seeds. Satsumaimo / Okinawan sweet potato flowers (I could have used my double flower cutter for this one, but instead I used a simple cutter for the flower, and cut out the center circle using a bit of straw -- easy and convenient!), purple cauliflower and tricolor tomato skewer. Fruit side has strawberries, raspberry, blueberries and plum.
This is quite a bright and colorful one! I think it might be the ultra-violet purple background ;)