My favorite combinations that I've used in my town are:
- Purple violets, white lilies, red roses
- Purple violets, white violets, blue violets
- Blue pansies, white roses, pink cosmos
- Black cosmos, white cosmos, orange cosmos
- Red lilies, pink lilies, white lilies
- Pink roses, white cosmos, purple tulips, black tulips
- Blue roses, pink roses, white roses, purple roses
- Red pansies, purple pansies, white cosmos, orange tulips, and black roses (for a more natural and random look)
Another combination that I think would look very pretty but I didn't find room for it is white tulips and purple pansies.
I like to use white as an anchor color. I feel like incorporating white into all of the different flower combinations makes the transitions easier and the whole town feels more cohesive to me without having to stick to a specific color scheme or type of flower.