Fingerglows

A fingerglow is a unique colour of a student's finger that reveals itself once their forest group leader unlocks their ability to use magic.

Use
When a student's finger lights up in their colour, 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.

Colours
While canon fingerglows are usually red, green, blue, or purple, it seems a fingerglow can be any existing solid colour 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 colours as time goes on. In book 3, Agatha notes that her and Tedros' fingerglow is the exact same shade of gold. This could mean that a student's fingerglow is the same colour as their true love's. If [School Master|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. [Lesso|Lady Lesso] and her son, [|Aric], are both described as having violet fingerglows, but Sophie and Agatha (who are twin sisters) have pink and gold fingerglows respectively. Maybe because Sophie is a Never while Agatha is an Ever, whereas both Aric and Lady Lesso are Nevers.

So far, 15 former students of the School for Good and Evil have confirmed fingerglows:
 * Agatha - Gold
 * Tedros - Gold
 * Sophie - Hot pink
 * [|Hester] - Red
 * [|Anadil] - Green
 * [|Dot] - Blue
 * [|Hort] - Blue
 * [|Vex] - Red
 * [Lesso|Lady Lesso] - Violet
 * [|Aric] - Violet
 * [|Callis] - Green
 * [|Beatrix] - Pink
 * [|Reena] - Purple
 * [|Millicent] - Red

Our 18 of our current students have confirmed their fingerglows:
 * [|Chaddick] - Silver
 * Alexandria - red-gold
 * Camella - black-gold
 * Gwendolyn - light blue with a hint of purple
 * Blanche - white-red
 * Lilian - watery-gold
 * Eden - light turquoise
 * Arbor - white-gold
 * Brooke - hot purple
 * Sebastian - gold
 * Rian - orange-gold
 * Quilo - crystal
 * Carol - icy blue-grey
 * Bree - lime green
 * Beckett- forest green
 * Hunter - navy blue
 * Cassia - pastel pink swirled with blue
 * Sloane - lavender
 * Charles - topaz

Trivia

 * Aside from Tedros and Agatha, not many Evers had confirmed fingerglow colours. 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 used to learn spells in her spare time.