How the figures were created...

1. Run MetaPost on a script like (this is for figure 1):

    beginfig(1);
    def blue = (0.5,0.5,1.0) enddef;
    def green = (0.5,1.0,0.5) enddef;
    def yellow = (1.0,1.0,0.5) enddef;
    u = 1cm;
    fill (2u,2u)--(2u,12u)--(12u,12u)--(12u,2u)--cycle withcolor blue;
    fill (10u,10u)--(10u,15u)--(15u,15u)--(15u,10u)--cycle withcolor yellow;
    fill (10u,10u)--(10u,12u)--(12u,12u)--(12u,10u)--cycle withcolor green;
    pickup pencircle scaled 1pt;
    for i = 1 upto 16:
      draw (i*u,0)--(i*u,17u);
      draw (0,i*u)--(17u,i*u);
    endfor
    pickup pencircle scaled 8pt;
    draw (2u,2u)--(2u,12u)--(12u,12u)--(12u,2u)--cycle;
    draw (10u,10u)--(10u,15u)--(15u,15u)--(15u,10u)--cycle;
    endfig;

2. Convert PostScript to PPM

    mv figures.1 fig1.eps
    pstopnm -xmax 200 fig1.eps

3. Add a margin and convert to GIF

    pnmmargin -black 1 fig1.eps001.ppm | ppmtogif > fig1.gif