Because the flavor of both shiso flower varieties is quite strong, but also very different, you may want to use them to garnish different dishes in the same meal if you want diners to eat them.
White Shiso Flowers:
The bold flavor of green shiso pairs very well with soy based sauces and dressings. Try pairing these flowers with raw fish (particularly sashimi), salads, tempura, and other dishes where you want a burst of bold flavor in a little, delicate, pretty package.
Green shiso’s fascinatingly complex flavor profile can be used in desserts as well, particularly those with citrus fruit, melon, or pears.
Purple Shiso Flowers:
The spice-like flavor of purple shiso pairs well with acidic ingredients like vinegar, citrus juices, and white wine. However, it’s important to remember that many flowers don’t react well to direct content to high-acid ingredients. So if using a high acid dressing on salads containing shiso flowers, test it on a few blossoms ahead of time and/or add it at the last second.
Edible Flower Recipes, Tips & Information