Do you have a window sill with an eastern exposure, or can you pull the plant back a few feet from its present location?

The more light variegated plants get, the whiter the leaves. Less light = more green.

Yes! I’ll pull it back a few feet and see what it does.

I wouldn't move it either. Strong variegation is a good sign that it is happy with the amount of light it is getting.

Thank you both! I’ll keep it with its friends on the windowsill then.

we have a new leaf since my first post and he’s looking great

BUT

Something is causing the older leaves to decay from the leaf tips in. It happened to a lower leaf (not pictured) while I was out of town and I thought it might have been caused by cold damage since the tip of the leaf touching the window during a cold spell. That leaf turned soft and brown from tip to about halfway, and I eventually got tired of watching it die and snapped it off. I rotated the plants so that all the leaves weren’t touching the window.

Fast forward to now, it has been a few weeks and I’m noticing the same sort of damage to the next leaf from the bottom. Two dark spots on opposite sides. They’ve been growing and I assume they will continue until I interfere.

What could be causing this?

You're over-watering, and/or, there is a high level of dissolved solids in the soil. You would do well to monitor your plant's moisture needs more carefully, and only water when it actually needs water. The top 2-3 inches of the soil might be dry, while the bottom 3-6" might be 100% saturated. Since roots need oxygen, this is an unhealthy arrangement, from the plant's perspective.

In many cases, we can judge whether or not a planting needs watering by hefting the pot. This is especially true if the pot is made from light material, like plastic, but doesn't work (as) well when the pot is made from heavier material like clay, or when the weight of the pot precludes grabbing it with one hand to judge its weight and gauge the need for water.

Fingers stuck an inch or two into the soil work ok for shallow pots, but not for deep pots. Deep pots might have 3 or more inches of soil that feels totally dry, while the lower several inches of the soil is 100% saturated. Obviously, this type of situation cause the loss of a very notable degree of potential. Inexpensive watering meters don't even measure moisture levels, they measure electrical conductivity. Clean the tip and insert it into a cup of distilled water and witness the fact it reads 'DRY'.

One very reliable method of checking a planting's need for water is using a 'tell'. You can use a bamboo skewer in a pinch, but a wooden dowel rod of about 5/16” (75-85mm) would work better. They usually come 48” (120cm) long and can usually be cut in half and serve as a pair. Sharpen all 4 ends in a pencil sharpener and slightly blunt the tip so it's about the diameter of the head on a pin. Push the tell deep into the soil. Don't worry, it won't harm the root system. If the plant is quite root-bound, you might need to try several places until you find one where you can push it all the way to the pot's bottom. Leave it a few seconds, then withdraw and inspect the tip for moisture. For most plantings, withhold water until the tell comes out dry or nearly so. If you see signs of wilting, adjust the interval between waterings so drought stress isn't a recurring issue.

Al

I can go pretty long between watering, but the pot is on the deeper side. I’ll try and find a dowel to use before my next watering.

Why is only one leaf affected?

And is there a way to stop the current ailing leaf from deteriorating further?

I doubt it. The plant appears to be an unstable sport which is sporting further.

Here's what your plant should look like. http://www.onlineplantguide.com/Plant-Details/3077/

Kitty - the spoiled foliage is the result of the plant's inability to move enough water to keep its most distal parts (usually leaf tips and margins) properly hydrated. The result is, the death of tissue due to lack of water. That shouldn't be taken to mean there isn't enough water available in the soil. In fact, there is probably too much water in the soil, Too much water in the soil = not enough air = impaired root function, even though roots might be awash in a sea of plenty. Once cultural conditions can be stabilized such that the plant isn't being asked to tolerate what it isn't genetically programmed to tolerate, normal root function can be restored and the progression of tissue death in the foliage will stop.

I can see at least 2 affected leaves. It's difficult to pinpoint the exact reason only one or two leaves might be involved because there are several scenarios that might make those leaves especially vulnerable. The most likely reason is, roots attached to the plant on the side directly below the compromised leaves (and in older trees, branches) are functioning especially poorly.

Al