There are four different colour groups: Black, Cream, Golden, and Red.
All bases on the site fall into one of these colour groups.

If you were to cross two parents from the Black colour group, all of their subsequent offspring will have bases from the Black colour group. If you cross a Black colour group parent with a Cream colour group parent, you can end up with offspring from both the Black and Cream colour groups.

For breeding, you will want to do your best to match colour groups together. This way, you have higher odds of producing bases within the colour group you're looking for, whereas breeding in different colour groups can result in many different potential outcomes.

There are three different shades: Dark, Medium, and Light.
This is where the bases start to split up a bit more into their own categories.

Now, let's say you want to get a little bit more detailed with your breeding. You don't want just any Black colour group cub. You want one specifically with Black Dark genetics. Your best option would be to cross two parents with Black Dark genetics, such as Onyx or Slate.

The way that shades work is like so.

Dark x Dark = Dark
Light x Light = Light
Dark x Light = 25% Dark, 25% Light, 50% Medium
Medium x Medium = 15% Dark, 15% Light, 70% Medium
Dark x Medium = 50% Dark, 50% Medium
Light x Medium = 50% Light, 50% Medium

If you breed two Black Dark genetics together, you are guaranteed a Black Dark cub; the same can be said for Black Light. However, as you can see, breeding two different shades together has a chance of giving almost any shade, especially if you were to breed a Black Dark and a Black Light together. You could potentially receive offspring with almost any Black genetics base, though this does depend on the parents' bases themselves.

There are two different gradients: Countershaded and Solid.
Most bases are easily recognisable as to whether they are Countershaded or Solid.

Countershaded bases are bases that have more than one colour in its makeup. They can include bases that have a dark topline and a light underside, or a light topline and a dark underside.

Solid bases are bases that are completely or nearly the same colour throughout the entire base. Don't be fooled, though! Solid bases can have different colours, and even some shading details. They're just more "solid" all throughout.

Breeding with gradients is a bit simpler than shades.

Countershaded x Countershaded = Countershaded
Solid x Solid = Solid
Countershaded x Solid = 50% Countershaded, 50% Solid

What the above means is that if you cross two Countershaded parents, all offspring will be Countershaded. If you cross two Solid parents, all offspring will be Solid. If you cross a Countershaded with a Solid, you can have cubs from either gradient!

Finally, there are four different rarities: Common, Uncommon, Rare, and Special.

Common bases are mostly made up of bases that can be found in explore on NCLs as well as rolled males. Most Oasis-applicable bases are classified as Commons.
Uncommon bases are certain bases that can only be applied via customising and the Oasis.
Rare bases are bases that can only be achieved through breeding with Uncommon, Rare, and Special bases.
Special bases are the most difficult-to-breed bases on Lioden. These include event applicator bases, combo bases, NCL-exclusive bases, and raffle-exclusive bases.

Rarities are passed much differently when compared to colour groups, shades, and gradients. Below, we have included a guide to indicate your relative chances when breeding different rarities together. Keep in mind that this particular guide is not relevant for hybrid bases (Kimanjano and Mandarin), as these have lowered pass rates.

The Uncommon and Rare rarity categories have the exact same pass rate as each other. The only difference between Uncommon and Rare bases is that Uncommon bases can be applied via customising and the Oasis, while Rare bases can only be bred for.

Special bases will never pass unless one of the parents is that specific Special base. Your highest odds of producing a Special base would be to breed together two Special rarity lions. It's worth clarifying that colour group, gradient, and shade crossings do not affect Special rates. Pairing two Specials in the same colour group or two Specials in differing colour groups both have the same 4% chance to produce a Special base. While the overall amount of Special bases produced will be the same, if you're aiming for a specific Special base, it is always best to pair two identical Special bases rather than two differing Special bases—this is because the 4% Special chance would be split between two bases. If you just want Special bases overall and do not care which one passes, then it does not matter which Specials you pair together, as you have the same chances to get Specials as pairing two identical Specials.

To give an example of breeding between different rarities, let's preview the possible outcomes between a few different bases.

As you can see, breeding a Black Dark Countershaded Common parent to a Black Dark Countershaded Rare parent can potentially produce cubs with Black Dark Countershaded Common, Uncommon, and Rare bases.
However, breeding a Black Dark Countershaded Common parent to a Black Dark Countershaded Special parent, while they can produce Black Dark Countershaded Common, Uncommon, and Rare bases, can only potentially produce that specific Special base that one parent has (in the example above, Celestial).

Breeding two different Black Dark Countershaded Special parents together can potentially produce any Black Dark Countershaded Common, Uncommon, and Rare bases, as well as having a chance of producing either Black Dark Countershaded Special bases from the parents (in the example above, Celestial and Divine).

TL;DR: A Celestial will not pop up when breeding two Slates together; however a Slate can pop up when breeding two Celestials together!