Preheat oven to 350 degrees. Grease and line three 8-inch round cake pans.
In a large mixing bowl, cream the butter and raw sugar until fluffy using a stand or hand mixer.
Add in the eggs one at a time followed by the canola oil, vanilla extract and lavender oil (if using).
In a separate bowl sift together the flour, salt, baking powder and dried lavender.
Alternate between adding the dry ingredients and the milk into the mixing bowl until a smooth batter is formed.
Divide the batter between three bowls and add the food coloring. For the light purple add two drops each of red and blue, for the medium purple add five drops each of red and blue and for the dark purple add ten drops each of red and blue. Stir until evenly colored.
Pour into the three cake pans and bake for 20-25 minutes, or until the top bounces bake to touch. Let cool while you prepare the frosting.
For the lavender buttercream:
In the bowl of a stand mixer add the butter, sugar, vanilla, lavender oil (if using) and dried lavender. Beat until light and fluffy, about ten minutes.
Use the white frosting to frost a crumb coat layer, beginning with the dark purple layer and ending with the light purple. Let firm in fridge while you prepare the colored frosting.
Divide remaining frosting into three bowls. For the light purple add one drop each of red and blue, for the medium purple add three drops each of red and blue and for the dark purple add eight drops each of red and blue. Stir until evenly colored.
Once the crumb coat is firm, spread a layer of the dark purple buttercream around the bottom, followed by the medium around the middle and the light purple around the top.
Using a cake scraper or cake spatula, turn until smooth. A cake turntable will make this step much easier, but feel free to go for a rustic swirl look.