set terminal png size 1280,720 enhanced font "Sans,15"
set output "diagram.png"
set pointsize 3
set xrange [0:10]
set yrange [0:10]
plot "< awk '{if($3 == \"red\") print}' dat.dat"   u 1:2 t "red"   pt 4, \
     "< awk '{if($3 == \"green\") print}' dat.dat" u 1:2 t "green" pt 4, \
     "< awk '{if($3 == \"blue\") print}' dat.dat"  u 1:2 t "blue"  pt 4, \
     "< awk '{if($3 == \"red\") print}' centers.dat"   u 1:2 t "red"   pt 7, \
     "< awk '{if($3 == \"green\") print}' centers.dat" u 1:2 t "green" pt 7, \
     "< awk '{if($3 == \"blue\") print}' centers.dat"  u 1:2 t "blue"  pt 7