Start by steaming your kabocha or orange sweet potato. Cook until tender, then push through a sieve to achieve a smooth purée. Let sit aside and cool.
Next make your dango. Gradually add water as you mix your flour in a large bowl with chopsticks. Once all of the water is added to the bowl and the dough thickens, you should be able to start to use your hands. Add more flour or water as needed (brands tend to vary, and the amount you may need also depends on the humidity!). The dough is ready when it's firm, smooth and easily workable.
Divide the dough into 15 equal pieces and roll into tight balls.
Set aside 2 of the balls of dough and knead in your pumpkin purée (about 1 tbsp) to add colour. You may need to add additional flour depending on how moist your pumpkin is.
Bring a pot of water to a boil, then gently add all of your dango to the pot. Stir with chopsticks occasionally to avoid sticking. The dango is ready when they start to float to the top.
Prepare an ice bath and drop your cooked dango gently in to cool and firm up. Strain, and transfer onto a plate or tray.
To assemble, arrange dango in layers of 9, 4 and top with 2 orange dango!