Underbelly

Underbelly is a common gene in which the fur along the underbelly or extremities is paler than elsewhere. It can cover the underbelly mane and tail mane, when present, but doesn't have to affect it entirely or at all. While it may have portions that are blurred, the majority of the marking should be fairly hard-edged, showing a clear distinction between it and the base coat or markings around it.

Underbelly is an optional two-toned marking, meaning that it can have two separate tones, though the paler of the two should always be closest to the underbelly or toes/tail tip, whichever is closer. For example, you should not have a darker colour on the feet and a lighter colour above it

Direct Inheritance

Underbelly also allows for some direct inheritance in coloration.

An exception to this rule of direct inheritance is of pure genos - those who were generated via items being the most common source. These may inherit the specific colour from the underbelly marking of any applicable ancestor visible in their tree, even if it is not a direct parent.

The closest to the extremities9/belly line should still be the lightest.

Clarification: Holes

Something we see a lot in the approval queue is misunderstandings over the "no holes" rule as well as the "extremities first" spreading rule. This means that feet, face, and tail tip (etc) should not have holes where the marking isn't present, unless those holes are connected to the larger area of marking-absence on the back.