Each heart level accumulates up to 5 hearts, the more hearts the biggest the level in that heart color
For heart levels Purple to Orange each time the character accumulates more than 5 hearts they'll automatically move to the next color, starting from 1 heart once more
If a character is at Gray level accumulating more than 5 hearts will result in going to the Black level, to go to Purple the hearts at Gray stage must be less than 1.
Red level is locked for family members, people who become family through whatever means (adoption, blood brotherhood, marriage, etc).
Characters accumulate hearts through a point system, for a template of how points are added up check here.
isthefootsteps [Higurashi no Naku Koro ni] "Quote" WIP Relationship: