The Tan and fox varieties are distinguished from other varieties by the belly colour, which is golden red in tan and white in fox. Tan is recognized in all colors, fox in only certain few.
at/at cch/cch, at/a cch/cch
at/at ce/ce, at/a ce/ce (beige) fox)
at/at ce/c, at/a ce/c (bone fox)
Foxes are recognized in self and silver-ticked varieties. This excludes white-bellied pointed varieties from being entered in shows, as well as white-bellied ticked varieties.
Recognized fox varieties can be divided into two categories by their genetic make-ups; chinchillated tans and extreme dilution tans. Black, blue, chocolate and lilac foxes have cch/cch, (black eyed) bone and beige foxes ce/ce.
One shouldn't try to breed chinchillated Foxes and extreme dilution Foxes together, as it would bring cch/ce Fox mice, with top colours something else than recognized fox varieties...
Red "foxes" are genetically something completely different altoghether. They are genetically Ay/AW - C/*, which can make the belly white on a red (or just make the belly colour bad for a red) - or exceptionally sharply demarcated red berkshires.