I have a blue stain on my carpet!

Any hints?
I pulled off the glove box, but it appears that I'm looking at maybe the AC...?

From an old audifans post:
Replacing the Heater Core. 80-87+ 4ks, 4kq, Coupe GT & ur-q
READ COMPLETE PROCESS BEFORE STARTING...

1) remove passenger kick panel/evap cover. 1 screw into drip tray, 1
screw into center console.
2) remove glovebox. 2 or three screws up into dash. 2 screws into center
console (forward edge in a recessed hole and down near the lower left corner
of the glovebox). 1 plastic screw/plug thingy in upper right corner. Rotate
plug so notch points to 3, 6, 9 or 12 o'clock (don't remember which one)
pull straight back and out.

If car doesn't have AC, steps 3 - 5 may not apply.
3) remove plenum/engine bay rubber seal and black plastic plenum cover.
4) remove (white) airbox cover from plenum. 2 screws on each end. Unplug
wiring and vacuum lines as necessary.
5) (re)move AC evap for clearance as necessary. 2 screws up into
firewall/plenum from footwell. 2 screws down into evap from plenum area.

6) drain coolant as desired. a) drain system, b) pinch lines between
motor/core and motor/heater valve. remove hose from heater valve to core,
drain core some(!) from this hose.

Note: recommend replacing heater valve, heater core hoses, and firewall hose
grommet while replacing heater core.

7) remove heater core cover from passenger side of airbox, in passenger
footwell.
8) find and loosen hose clamps to heater core.
9) remove heater core hoses from core. !! Have rags handy, this will
spill coolant !! Plug core in/outlets??
10) push core hose into engine bay if replacing.
11) remove heater core. Move AC evap as necessary. This may require some
brute force or opening of the AC system by separating the two AC lines. If
you're not comfortable with brute force and your AC is charged, consider
having AC evacuated before beginning this procedure/disabling your car.
Recharge after the job has been completed. Seal the AC lines if you do end
up separating them.
12) Installation vaguely resembles reverse of removal.

Make sure the core is installed with insulation to prevent cold air going around the core.

Thanks!