To get a clearer picture:
The cream gene does the following:
Take one bay horse and dip it into bleach one time you get buckskin; dip twice and you get perlino
Take a sorrel and dip one time into bleach you get a palomino; dip twice and you get cremello
One black horse dipped once into bleach you get smoky black; dip twice and you get smoky cream...
Dun Factor is a completely different gene and affects base color (bay, chestnut, black) as follows:
Bay horse + dun factor = Bay dun, classic dun, or zebra dun (I have this kind of dun gelding) This is a yellowish tan body with darker points (mane, tail, legs)
Chestnut horse + dun factor = Red dun, claybank or fox dun (this is a reddish horse with darker red points as there are no black points to dilute)
Black horse + dun factor = Blue dun or grulla/o (my favorite!) and is smoky, bluish, or mouse brown and vary from light to dark.
Now here's the kicker... A dun horse MUST HAVE A DORSAL STRIPE or it is not a dun, no if's, ands or butts. They also may have primitive markings such as leg barring, shoulder bars and face cobwebbing... However, if a horse has a dorsal stripe (as in some buckskins) it does not mean it's a dun... This can be 'countershading' as some foals are born with this, but the markings disappear as they get older...
Or, read this website - everything you ever wanted to know about dun factor but were afraid to ask
http://grullablue.co...or_markings.htm
Other dilute genes can also have an affect on the dun factor gene, i.e. silver or cream, but that's a whole other ball o wax and can make your head spin!
Kari