You have a fungal pathogen at work, most likely one of the several genera loosely placed under the umbrella of damping off diseases. Suspect point of entry into the plant to be via the root system or as a result of watering practices that splashed soil containing the pathogen onto the leaves or stems. It's likely going to end in loss of the plant's viability, and starting cuttings will likely not produce satisfying results due to the existing infection, but you can try.

Be sure to toss the pot or sterilize it before planting anything else in it. The spores can remain dormant in detritus that clings to the pot for years.

Al

@tapla (mid-Michigan, USDA z5b-6a), is that infection from the white discoloration or the black specks?

It's from an invisible fungal pathogen that might be from any of several genera - Rhizoctonia, Pythium, Phytophthora, and Fusarium being the top candidates ...... might as well include Botrytis, too. Necrotic (dead) areas on leaves and stems are only symptoms which indicate the disease is at work.

If the creamy white coloration on the leaves isn't a genetic trait, it's likely a symptom of what plants do during the resorptive phase of leaf abscission (shedding). During this phase, the plant reclaims (think 'recycles') mobile nutrients and other biocompounds for use elsewhere in the plant. Example: Magnesium (Mg) is central to the chlorophyll (a green pigment) molecule and easy for the plant to reclaim. When the Mg is removed, the chlorophyll molecule is destroyed, which means the green coloring is removed, which allows other pigments to become expressive. This process plays a large part in the change in leaf coloration in autumn before leaves fall.

Al

@tapla (mid-Michigan, USDA z5b-6a) ok, thank you. Because mine has some white discoloration but is otherwise very healthy, and no black spots. I'm mostly curious because it's got 3 flower spikes right now and I'm wondering how concerned I should be. I had thought it might be because it was getting a little bit of a draft from the window.

I beg a pardon, MPHN. I thought I was replying to the original poster/author and answered your questions based on the images provided along with the original post, so what I said might not be applicable to your questions at all. My bad for not paying closer attention.

I just seconds ago I noticed another post of yours that went unanswered except for the gracious reply provided by Rina from Ontario. Based on what I've seen of your participation so far, I think you might find this thread interesting. It provides an Overview of Good Growing Practices, which if adhered to will allow you to sidestep most of the barricades other growers usually hit head-on along the path to proficiency.

Al