a 4Female and 10Male produced a 7F, but it also can produce a 6 or a 8, but a 5 or a 9 happens very rarely, but keys to get more blondes and brunettes are:

9Male+22Female=29Female
15Male+14Female=9Male
10Male+9Female=18Male
29Female+9Male=18Male
29Female+18Male=9Male

hope it helps!