Full sun would scorch them and turn the leaves in direct contact with the sun all yellowish or all whiteish, including the leaf veins (leaves protected from the sun would look fine).

The leaf infections to look out for are cercospora and anthracnose but the damage does not fit the bill with the pictures I have seen before. Perhaps the disease is not advanced enough. Are all leaves affected or only some?

See the link below.With fungal infections, make sure you do not use overhead watering of the shrub and instead, water the soil early in the mornings. You can dispose of infected leaves and blooms in the trash (not a compost pile).

If you confirm, consider using fungicides recommended by ACES (see the link below) since it is early in the season for this type of problem. You can always take the leaves in sealed plastic envelopes to your agric extension offices or local universities for proper analysis/diagnosis.

Here is a link that might be useful: Diseases of hydrangeas

You may have spider mites. Look at the bottom of the leaves and see if you see any tiny critters.

HI luis_pr, in certain area but slow spreading. I sprayed some fungicides this morning. We shall see.

Hi kidhorn, no tiny critters underneath.

Good morning, Joopster. Reading kidhorn's comment, I was thinking aphids could also be a match to the black stuff. Aphids excrete honeydew which, in time, will convert to a black sooty mold fungus.

Contrary to mites, aphids are not hard to see, are larger and more visible than aphids. They are sortof kindof whiteish/sandy-ish/yellowish, almost transparent in some cases but... not always. You can so a search in Yahoo or Google for "what are aphids" to see pictures and information. They tend to be visible, in bunches though, along the stems sometimes, and they can cause new growth to curl. I release lacewings or ladybugs in May to combat them near my roses as they also like to bother the roses' flower buds.

Affected leaves where the fungus has not converted the honeydew into mold will look kind of wet from some angles and "with something sticky" too.. Honeydew is excrement so wash your hands if messing with aphids.

I inspected the plant again after being away from home for a week. No bug, no insect found. I did sprayed some Fungicide and some insect sprays. She looks ok. The infection did not spread to other hydrangeas next to it.