Diane - my guess they are cold. Just this time of the year when you stop your furnace (not today, no-no). Usually the cooler it is - more white the variegated leaves become. It will warm up - and they will get greener. You can as well give them a fish emulsion drink.

I do not know what stiff and hard means. Keep an eye on them, may be it will resolve on its own when the weather will warm up. You can always increase the humidity by covering your plant with a plastic dome (angel cake top for example) and see how it goes - it is like a spa treatment. Could be low humidity, could be to0 much light.

Good Luck and keep us posted

Irina

Hi,
I don't think that it is a problem with too much light. North windows don't give you that much unless you are below the equator. More likely than not I suspect that the plant is cold as Irina said. Try moving it to a warmer area with a western exposure and give it a shot of fish emulsion.
Fred in NJ