Using the graphics pages to store data

OPTION STRICT
OPTION DEFINT

DEF WR _N,X,Y
 DIM A,R,G,B,N=ABS(_N)
 A=(SGN(_N)==-1)
 R=N DIV 31 DIV 31*8
 G=N DIV 31 MOD 31*8
 B=N MOD 31*8
 GPSET X,Y,RGB(A,R,G,B)
END

DEF RD(X,Y)
 DIM A,R,G,B,N
 RGBREAD GSPOIT(X,Y) OUT A,R,G,B
 N=R/8*31*31+G/8*31+B/8
 IF A THEN N=N*-1 ENDIF
 RETURN N
END

I never really bothered screwing around with color codes and color conversion before. This method covers the integers from -30751 to 30751. Is there a better way?