| Spoiler warning!|
This article contains plot details about one of the books. You have been warned.
When a student's finger lights up in their color, it means that they have summoned enough emotion and purpose in order to cast a spell. When students graduate or demonstrate a certain level of control over their abilities, their glow is "re-locked" by the school, as it is considered embarrassing for one's finger to glow every time they cast a spell.
While canon fingerglows are disproportionately red, green, blue, or purple, it seems a fingerglow can be any existing solid color or shade. A fingerglow that is black, silver, gold, periwinkle, vermillion, etc. is possible, but a fingerglow that is "black and white," or "blue and pink," or "rainbow" is not.
Fingerglows can also change colors as time goes on. In book two, Agatha notices that her fingerglow has changed its color, being gold instead of orange. In book 3, she notes that her and Tedros' fingerglow is almost the exact same shade of gold. This could mean that a student's fingerglow is the same color as their true love's. However, she originally described her fingerglow as orange, meaning a couple's individual fingerglows could start out as completely different colors and begin to resemble each other as they become closer. If Rafal's claim that he is Sophie s true love or Hort's prediction that he will marry Sophie is to be believed, a fingerglow could also be simply complementary to one's true love.
Fingerglows also seem to be hereditary, to an extent. Lady Lesso and her son, Aric, are both described as having violet fingerglows, but Sophie and Agatha (who are twin sisters) have pink and orange (later gold) fingerglows respectively.
- Aside from Tedros and Agatha, not many Evers have confirmed fingerglow colors. This is because aside from mogrification, the School for Good tends to downplay sorcery and teaches princes to fight with weapons (swords, bows & arrows, etc.) and princesses to rely on the help of animals. Agatha sees this a disadvantage and makes a point of learning "Evil" spells in her spare time.
- So far, 11 characters have confirmed fingerglows: