The natural question is, of course: Why?
The bloodline system is perhaps Mortal Online's most innovative and unique RPG system, allowing an unprecedented amount of control when it comes to allowing a player to mix ancestries within a species. Even single-player RPGs fail to capture this realistic element of biology, culture, and history—it could easily be one of the features to make Mortal Online stand out as unique and gain the game a lot of attention for how interesting it is and how much power of customization it puts into the players' hands.
At the moment, however, this extremely unique system is invisible aside from size, and only impacts stats. Someone who is half-Sidoian and half-Kallard will either look entirely like a Kallard or entirely like a Sidoian—when they're actually both and neither. Due to the extremes of either side of their ancestry, this character should likely look distinct from both bloodlines.
The systems I'm proposing would allow for both players and NPCs to look the part of someone mixed with what they are.
For players, this means a greater variety of options and control when it comes to their characters, while also entirely sticking with the lore and intended aesthetics of each race. It doesn't allow them to suddenly look entirely unfitting for their ancestral choices. Their choice of race will matter in how they appear, instead of being 1/4 Tindremene, 1/4 Sarducaan, 1/4 Sidoian, and 1/4 Khurite—and looking identical to a Tindremene, as it is now.
For NPCs, this is a powerful tool for StarVault when it comes to creating characters and representing admixture in NPC populations.
In the region of Varborg in Nordveld, the majority of the population would be a mixture of Tindremenes, Kallards, and maybe Khurites (or even Sarducaans) as well. With the current system, one could only get Tindremenes or Kallards in appearance, but if admixture was visible then many of these NPCs could be set to be any mixture of Tindremene, Kallard, and Khurite—and they could look the part without Starvault having to design special models/textures for them. This NPC population would then look distinct.
Sidoian noble families have been written into Tindrem's lore by Mats, including how they gained this status following the Irruption. Some of these families have likely mixed with Tindremenes over the years, which would result in some of the Sidoian families of Tindrem having members wandering the streets that look similar to characters like Missandei from Game of Thrones or the character Markus in Detroit: Become Human.
Among the Khurites, many of whom purposefully have children with outsiders, there would likely be at least a small mix among many NPCs. Myrland Khurites may have 1/4 Tindremene members common among their ranks, while Sarducaa Khurites may frequently have 1/4 Sarducaans, and Nordveld Khurites may have 1/4 Kallards.
Used for: Eye Color, Hair Color, Hair Texture, Face
Every ¼ of ancestry would give 1-10 points towards a specific option I call a 'trait', and once a trait reaches 10 or more points, the option appears as available for character creation (or gains a chance to appear on a randomly generated NPC).
As an example of this, Tindremenes may add 3 points to a bright red hair color trait, and Kallards may add 3 points towards this trait as well, while Sidoians have 0 towards this trait.
This means that one can be any combination of Tindremene/Kallard and have this hair color, however, because Sidoians don't give any points towards bright red hair, one cannot be 3/4 Tindremene (+9) and 1/4 Sidoian (+0) because it fails to break the threshold.
This specific method was thought of so that it would allow multiple ancestries to push towards the same trait, rather than dividing everything up by specific 1/4ths of ancestry and possibly creating a situation in which a 1/2 Tindremene and 1/2 Kallard couldn't have a hair color that both ancestries have when full-blooded. TL;DR: It allows multiple ancestries to contribute towards the same trait.
Used for: Human and Thursar Skin Colors
For options that exist along a gradient, the 'Blending' system would combine numbers and average them, very similar to how it's already done for stats when blending bloodlines.
As an example, if Tindremenes have a number of '2' and Kallards have one of '4', then these numbers would average out to 3 in a character that's 1/2 Tindremene 1/2 Kallard.
As this only applies to Skin Tone and Humans/Thursar, further explanation is within that page.