If regular Brovi pigments are too cool and saturated for your client, you can mix them with Brovi+ in 50/50 proportion.
However, that rule doesn't apply to Gray Harbor and Freckle. These pigments won't change color when mixed with their Brovi+ correspondent pigments.
If Brovi+ pigments are very light for your client, you can add a corresponding color from the Brovi line and mix them together. For example, you can add 7 drops of regular Roasted Chestnut to 3 drops of Roasted Chestnut+ (you may adjust the proportions depending on the desired saturation).
You can mix the opposite colors from Brovi+ line. For example, Gray Harbor+ & Bitter Chocolate+. When mixing these colors, you will receive a neutral brown color that will look natural when healed.
There is no sense of mixing Roasted Chestnut+ & Bitter Chocolate+ because both colors have a warm orange base. Also, you shouldn’t mix any color from Brovi+ line with Freckle+ or add corrector, because this line is already very warm.