Mine have done the same thing. Not all of them
but about 3 of the 6 that I put in pots.
I have discovered that once they start turning
pink, they are doomed.

Update: I took some that were starting to turn pink
and placed them outdoors, in a shady area, (they were
growing under flourescent lights up until then). After
about a week I noticed new green leaves in the center,
so I plucked off the pink ones and the plants are starting
to look healthy again. Must be a 'light thing'.

Pink or red leaves can be a sign of not enough light, too little or too much water, being pot bound or the dreaded blackleg. If it is blackleg they are indeed doomed. Geraniums like to be grown on the dry side so pink leaves from too little water is preferable to getting the fungal desease blackleg.

When I see them the first thing I do is look at the stem just above the soil if it is discolored--mainly brown or black that is blackleg and there is nothing you can do but discard it because there is no cure and it could spread to your other plants.

I had the same problem. found out it could be a Magnesium deficiency. I watered them just one time with a solution of 1 tsp epsom salts to a gallon of water. The old leaves didn't recover, but the new ones look healthy.
I snipped off the old leaves that were damaged.
Seems like the orbit varieties were affected more. The black leaf collection, not at all .
also, geraniums are heavy feeders..I changed to a fertilizer with more Nitrogen for now.
NOw theylooke sellable.

Before going to extremes of 'why', try instead removing them from constant sunlight or reduce their intenseness of light.
Often leaves will burn from incrased amounts of sunlight that they are not acclimatized to.
Give them incrased amounts as days progress, bringing them back out of the light during nighttime.