\documentclass{standalone}
\usepackage{luamplib}
\begin{document}
\begin{mplibcode}
beginfig(1);
color brg, pbr; 
brg = 1/256 (1, 66, 37);  % British Racing Green
pbr = 1/256 (223, 52, 57);  % Pillar Box Red
N = 5; n = 0;
for y=1 upto N:
  for x=1 upto N:
    fill fullcircle scaled 16 shifted 20(x,y)
      withpen pencircle scaled 2
      withcolor (n/N/N)[pbr, brg];
    label(decimal incr n infont "phvr8r", 20(x,y)) 
      withcolor white;
  endfor
endfor
endfig;
\end{mplibcode}
\end{document}