The state_adaptive_color may be used to visually associate a displayed state with a corresponding graph:

type: custom:mini-graph-card
entities:
- entity: sensor.cleargrass_1_temperature
name: Temp
show_state: true
color: red
state_adaptive_color: true
- entity: sensor.cleargrass_2_co2
name: CO2
show_state: true
color: green
state_adaptive_color: true
y_axis: secondary
show:
name: false
icon: false
If some point is selected on the 2nd graph then the left "state" text contains a value for this point:

This confuses since the label has a value for the 2nd entity and a color for the 1st entity.
Suggestion:
If some point is selected for some entity and this entity has the state_adaptive_color: true option, then set the text color accordingly to this entity.