Word or phrase for making something seem better by comparison

The name for something that is used to make something else look different by comparison is a foil:

foil, noun. Anything that serves by contrast of colour or quality to adorn another thing or set it off to advantage.

The presence of a foil induces a cognitive bias known as a contrast effect.

I'm not aware of any terms that mean to create a foil or to induce a contrast effect.

Watson is a perfect foil for Holmes because his relative obtuseness makes Holmes's deductions seem more brilliant.

[Britannica Online]

(emphasis mine.)

Differentiated.

The lemon starburt differentiated cherry from other flavors.

You can say something like: "The lemon Starburt was created to make cherry flavor seem tastier by comparison."