"Going full hair platinum" means completely lightening your hair the lightest shade of blonde, a nearly white, icy color often described as "platinum blonde," which requires significant lifting to achieve, resulting in a dramatic, high-maintenance look.
Foilayage is a combination of balayage with the use of foils more often seen in the traditional application of highlights to create brighter, lighter sections throughout while retaining a natural-looking finish and seamless blending.
Book this technique for highlighting hair in which the dye is painted on in such a way as to create a graduated, natural-looking effect.