A double process application involves the application of a:

In the context of hair coloring techniques, a double process application specifically refers to the method used to lighten the hair before applying a tone or color. This technique generally involves two distinct steps: first, the hair is lightened using bleach and developer, and then a toner or tint is applied to achieve the desired shade.

This process allows for a broader range of color possibilities by first lifting the natural pigment to a blonde or lighter base before adding a new hue, which can help neutralize unwanted undertones or enrich the color. While toner or tint is indeed part of the double process, the focus here is that the whole process encompasses both steps of lightening and coloring.

The distinction with other choices lies in that while bleach and developer is essential for the lightening phase, the concept of a double process as a whole includes the application of toner or tint as the second step, thus making it critical to recognize the emphasis on achieving the final tone or hue in the overall process.