Grayish areas on a leaf may be caused by frost damage. If the plant variety is too tender or the plant has not hardened off and is hit by an early frost, this may occur. Application of fertilizer after mid-June my stimulate tender growth that is frost susceptible.

It could also be wind burn. That happens when the roots are frozen or just too dry and the plant is exposed to sun and wind and the leaves get dessicated. The solution is to mulch and provide a wind break and some shade.

Being still in their containers they are more at risk. The mulch would need to surround the entire container.

Wind Burn:
{{gwi:400518}}Sun Burn:
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Here is a link that might be useful: How to grow rhododendrons and azaleas.

Ojoy, in what climate zone are you located, and is this a covered patio or porch? It looks more dry to me than cold, have you been continuing to water if you are in a mild area?

As Rhodyman points out, it will be more susceptible to winter wind if not given adequate water.

We did recently have some really nasty wind storms that even knocked out the power. However these plants are just a few feet from each other, i.e. on either side of my front door:
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This is how the azalea looked earlier this year. It is up against my cat's kitty condo which is basically an enclosure which I draped in sheer fabric. The one out of view is the azalea that now looks healthier.

The azaleas are on a patio that has a deck overhead that extends for several feet, i.e. the patio is covered but not enclosed. Actually it is interesting that the azalea that looks better is drier than the sad looking azalea. I am wondering if a problem might have developed with the drainage. The azaleas were transplanted into new containers. They aren't in the original containers.

But do they have drain holes and good drainage? This is important. The damage looks more like sun & wind damage. They may be greenhouse plants which don't tolerate outside weather very well. This side of the porch may get more wind than the other side. Also, the winter sun is at a lower angle and overhangs don't provide much shade.