Too much water and not enough nitroge, perhaps.
Cold is not the reason for yellowing in alliums.
As they say, alliums are heavy feeders.

Not enough nitrogen usually causes yellow tips, while too much heat and not enough water causes yellowing of the bottom leaves. Urea is a good source of nitrogen for alliums.

I too have some yellow leaf tips. The scapes just started growing, is it too late to apply some nitrogen, or will it affect bulb formation?

Whenever my alliums start to show yellow, I top-dress them with a generous helping of good compost, and they always recover.

Can you cut off the tips of alliums leaves when they turn yellow and cut off the totally yellow leaves off completely?