I have what is probably an odd view on peony vegetation. This is probably a bit zone dependant.
Foliage for a peony isn't especially important in terms of longevity. If you can get to August and still have green leaves, the root system is probably in good shape for pushing new stems up the following spring. This isn't to say that they are unimportant, but even the plant doesn't do much to regenerate it's foliage - it largely grows what it grows fairly early in the year, and that's it.
Because it doesn't regenerate/regrow leaves, they will, as time goes on, yellow, develop sunspots, get nibbled on, and will otherwise not look as luscious or as vibrant as it did in the spring. But the roots are growing and the core of the plant is very efficiently and very effectively becoming increasingly ready for the challenge of winter.
Regarding your photos, the leaves towards the window may look the way due to light reflected from both the glass and the light colored siding/paint. They are getting an extra dose of UV and are a bit toastier as a result. Overall, I think that your plant look fairly healthy.
If you do worry about sunburn and decide to increase the odds for your peonies, you could build some shade for the plants. I have a peony that is horribly burnt by the sun and I used 4 bamboo poles and a bit of ground cloth along with some clothespins to make an overhead canopy for the plant. You are not looking to blot out the sun - you just want to shield it during the peak of the day.
I also have had a peony that got mowed by early summer - two years in row. Yes, it didn't grow much, but it did continue to come back and is now quite healthy. Time beats up peony foliage - as long as stems aren't turning black, things are probably ok.
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