Indeed, until 2003, it was possible to take the then extant "primary magenta" (28350) and the "basic green" (28540) and mix them together into a neutral grey.
In the course of upgrading the product to AERO COLOR® Professional , the designation "basic colour" was struck out of the product assortment, but not the shade. Using the colours "primary magenta" (28304) and "brilliant green" (28501) it is still possible - with a mixing ratio of 1:1 - to create a comparable neutral grey.