Well, the easiest way is to create a dummy variable just for the subgroup (ie subgroup 1). Then with the help of the twoway scatter command you can have a graph like that in the picture.

          gen dummy=1 if subgroup==1
          replace dummy=0 if subgroup==2


After that
twoway  (scatter var1 var2 if dummy==1 , sort mcolor(blue) msize(small) msymbol(X) ) /*       
  */(scatter var1 var2 if dummy==0 , sort mcolor(red) msize(small) msymbol(triangle_hollow))

Try experimenting with the mcolor msize and msymbol values inside the brackets (i think that for your graphs msymbol has to be circle and circle_hollow respectively.

Hope this helps

It works!
Many thanks.
Best regards.