An apparatus includes a processor coupled to a memory. The processor calls a second function from a first function by coloring with an inaccessible color value a first memory area associated with the first function, branching to the second function, coloring with a second color value a second memory area associated with the second function, operating on the second memory area, and coloring with the inaccessible color value the second memory area. The processor then returns control to the first function, and colors with a first color value the first memory area. The coloring step includes branching to a coloring routine that includes a basic block beginning with a single branch target instruction, identifying and authorizing the calling routine, coloring with a hardcoded color value a memory area associated with the calling routine, and returning to the calling routine.