If you are satisfied with results just merge down the entire circles layer.
When you have one separate layer use layer stiles on it.

After that select a color range ? grays the are lighten.
Something like this. Layer via copy and overlay the new layer with white color.
Layer positions:
When you have one separate layer use layer stiles on it.

After that select a color range ? grays the are lighten.
Something like this. Layer via copy and overlay the new layer with white color.
Layer positions:
|
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