Tan is the wideband version of Otter that can come in Black, Blue, Chocolate, or Lilac. Unlike Otter, the undercoat of a Tan goes all the way down to the skin (which is a strong indicator of the genetics for true wideband).
Although Tan is most commonly known as a breed, it's also recognized in the US as a color in other breeds like Netherland Dwarfs, though not as many because it's difficult to develope. Deep, rich Tan coloring doesn't come naturally and has to be selectively bred for, it cane take many decades to remove light areas especially from the groin and tail area (which are naturally lighter than other parts). The desired standard is usually for a uniformally rich, red color throughout the markings.
On the D Locus
page, we went over the myth about breeding two dilutes together. This is a common misconception with Tans, since rich red coloration is usually desired in all four colors, but dilutes naturally have more washed out markings (making them seemingly less desirable). Fortunately, you don't have to worry about breeding two dilutes together, as this will not cause the offspring to be even more washed out. Although it can work out that way, it will have nothing to do with whether both parents were dilute or not. Its entirely dependent on other modifiers.
When breeding dilute Tans for rich color, Your best bet is to pick rabbits who have particularly bright deep markings regardless of being dense or dilute. If you three Black Tan bucks and one has deeper redder color than the others, it means he has the modifiers you want which will pass down to both dense and dilute offspring. Likewise if you have three Blue Tan bucks and one has deeper redder color than the others, he's the one with the deeper redder modifiers that can be passed both to dense and dilute offspring (regardless of his partner).