did you find out what the problem was? i am having trouble with foliage on geranium 'rosemoore' turning white from loss of chloropyhl. as if they are trying to variegate themselves. but no pattern, or consistency. smaller leaves go totally white.

Rich, fertile soil......and how old is it? Is it maybe been kept for long periods.
Rich soil is not always a medium that some plants need or want; many plants can do well in undernourished soil.
The loss of photosynthesis is attributable to how the roots feed the leaves....and isn't always just wanting sunlight.
Also, Europe (Mediterranean) is not semi-tropical; the sun does lose intensity the same as all northern hemisphere locales.
When the sun returns in February/March, plants renew growth rates.
This is why many gardeners overwinter geraniums in a cool environment, to the point that they are given no light, no heat, no water...until the sun begins its trip north. Its at that time they are cut back, given fresh potting soil, something under the roots so the plant drains well, watered to drainage, and a good sun...without being too close to a window which can cause sun-burn and heat the soil too fast.
I have no idea just what kind of sun plants get in southern Spain, but I suspect the plant is not receiving sufficent to maintain a healthy green leaf.

There are other causes of leaves losing their natural colour. Sucking insects, too much light, not enough fertilizer or the plant is receiving too high a temperature at night.
Since the plant, at this time of season, is not growing, giving it fertilizer is just a waste of time and money and does the plant no good. Only feed a growing plant.

Sometimes soil is allowed to dry too much. At this time, if the dryness is not corrected within a certian time, the soil shrinks from the sides of the pot. When you water, the water then goes down the sides into the drainage saucer. The gardener sees it there and thinks the plant has received adequate water, when, in fact, it has received very little; the water has gone down without making contact with the roots. Water sitting in the drainage saucer, if not dumped in a reasonable time, is taken back up--giving the plant what it just got rid of...excess salts.
Always, dump the drainage water within a reasonable time, usually 10 to 15 minutes. Never use cold water or water that has gone through a softening system. Let the water gain room temperature by leaving overnight.

Just some of the things that can cause problems to houseplants and garden plants treated thusly.

It's a pH problem. The symptoms are referred to as Chlorosis. My guess is that your mix is too alkaline, causing the plant not to be able to absorb iron. We sometimes see it with acid loving plants that are in a high pH soil. Add some sulfer to your pots, or better yet, repot and make sure your potting mix is either neutral (7) or slightly acid (6.5).

Steve

Here is a link that might be useful: University of Illinos at Urbana extension service