How to change color of words in Gedit?

Question

I'm writing a code in CUDA C and I'm using Gedit as text editor; when I type some functions like sizeof(), the editor does not color them. In simple words this is what I would like to see:

#include <stdio.h>
#include <stdlib.h>

int main(){

int a = sizeof(int);
return 0;  
}

This is instead what i get: sizeof() not colored!! What should i do to modify the color of the function? i have already installed all the plug-in but I don't know what else to do...