Combo markings would be an acquired BO trait that appears randomly on combo cubs. They can only be passed from a combo-based lion and unable/rare to be rma'd.

Here is a picture representing combo markings, but in an easier format:
https://imgur.com/a/GXyeZc2


So let's put that in action,

I have a Sutekh king and breed him to an Inpu lioness. They have a lovely Ogdoad cub!
The Ogdoad cub has a 100%(or lower) chance to acquire a new Ogdoad marking in any empty slot, including hidden slots.
For example, say there's Ogdoad Cockled unders, Ogdoad sable, Ogdoad dim, and Ogdoad zebra. This cub happens to inherit Ogdoad Sable in slot 8, which previously had no marking assigned to it.
The marking can be removed and treated like any other mark.
The marking has the same pass rate as any other BO and can be used on raffle lionesses.

This benefits the realism factor of genetics too. It makes sense that a cub born from a combo would have some resemblance, right?

Why is this better than just another app?
- Combos are very hard to breed but cheap, this would make the process more rewarding and appealing, effectively saving some dead bases like Black Rose and adding hype to new ones like Hexaplex.
- This would create grounds for even more breeding projects. Such as breeding ogdoads until you can get Ogdoad zebra in slot 7, to complete a color bomb full-BO heir.

What about combos that already have marking sets?
Rime, Hoarfrost, Elysian, Ember, Gilded, Cloudburst, and Pulsar already have markings. They are gorgeous but common. That leaves mods with two options: make a new set of 4 BO marks alongside the app ones, or just let those cubs roll for the preexistent ones. I'm sure many of us would kill for a new set of Pulsar marks anyways.
Squall, Soul, Olive, Ogdoad, Ennead, Temporal, Snowflakes, Smog, Seraiah, Mistletoe, Majivu, Styx, Sphynx, Rose Gold, Nadir, Qahir, Mudstone, Madagascar, Black rose, Citrine, Hexaplex, Hellebore, Celsian, Cairngorm, Asiatic, Arabica, do not have marks yet. 7/26 combo bases have marks, wouldn't you want to see them get more love? Not only that, but many of these marks are perfect for colorbombs. There aren't many colorful BOs, so this could really become popular and add some spice to the raffle girls.
There are a ridiculous number of combos, so it would have to be a very slow process for all the bases to get markings.


What if I don't like combo markings?
Easy, remove them from the cub. These marks can only pass onto a slot that previously rolled empty. All of your project Breedings and rosette chances will remain safe. If a cub rolls all 20 slots full, the marking will not appear.