I used to look up there every time I wanted to trait my troops or to farm specific arcane traitstone when I was new to this game.
Now I know what traitstone a troop needed or where to farm it by looking at their mana color. Example: any troop with blue/brown mana need arcane shield traitstone. The amount is depends on base rarity of that troop. Legendary need 16 (10 for 2nd trait, 6 for 3rd trait), Epic need 12, etc etc.