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Each Troll has a different colour of blood. The colour of their blood matches the colour of the symbol on their shirt, although their are a few exceptions. The blood of a Lusus appears to be the same colour as its associated Troll, implying that it is a large factor in the selection of a Lusus.
There is a caste system on Alternia based on the colour of an individual's blood. The hierarchy follows a rainbow, with red being the lowest and purple being the highest. "Blue Blood" seems to be a general term describing all trolls with blue to purple blood, the general upper classes. Some of the trolls at that very bottom of the Hemospectrum, with red and orange blood, are known by the derogatory term of "Rust Bloods". Those with orange or yellow blood are sometimes called "Fudge Bloods."
The trolls with the highest blood colour of magenta and tyrian purple are Sea Dwellers who live underwater, sport fin-like protrusions on the sides of their faces, and rule over the rest of the troll species. The troll with the highest blood caste at the time of previous leader's death is named His or Her Imperious Condescension. The High Nobility, although land dwellers, have ties to the sea. The Lusii are often Sea Creatures, and their homes are often on the coast or on small islands.
Higher blood castes seem to have more lavish hives: Chynus' hive resembles a large castle or mansion, while Benjas' home is a lot smaller and less impressive. Dorian's hive however was so poorly constructed it was shaken to the ground in an earthquake.
The Jade blood colour is quite rare, it allows one to be highly resistant to the rays of the sun and even warrants the protection of a Virgin Mother Grub.
A troll's blood colour does have an affect on a trolls disposition. A Troll with a higher blood caste is much more likely to be angry and violent. Low bloods are often mellow and calm. This holds true for the Stemfazed Trolls, apart from with Chynus. As a High Noble, his blood colour would suggest that he is violent and even psychopathic. Initially many are wary of him for this reason, but those who get to know him realise he is perfectly level headed. <spoiler>Although it turns out later that he isn't an exception.</bullshit.html>
Lower caste trolls are far more likely to have psychic powers, but are more susceptible to psychic attacks. Dorian, as a peasantry troll, has moderate psychic powers, something that is completely normal for one of this caste.
It is possible that the blood-colour caste system may correspond with medieval class systems on Earth. Based on this supposition, purple blood would be high royalty, blue would be nobility of sorts, green would probably be lesser nobility, and red would be peasantry. The intermediary colours are harder to discern but may correspond to other roles in feudal society or may fall under the previously listed four groups.
Exact Caste Determination Edit
Although there are 12 possible blood types for trolls, there are ways picking a higher blood colour out of two trolls of the same caste.
There are two types of caste regarding hue, 'spectral' and 'absolute'. A spectral caste can have a multitude of different hues. For instance;
However, with some castes this cannot be done. For example, the 'nobility' caste can only have pure blue colours. It is absolute. Any deviation from this pure blue, and the blood will either fall under the caste above or below. In this instance, blood brightness must be used to gauge quality.
With pure red, 'peasantry' is an absolute caste. absolute then alternates with spectra; until the final caste, 'royalty' a spectral caste.