I want to share the latest on the USGS Color Aerials, which have shown some, well, inconsistent behavior as of late to say the least.
In version 4.6.0,I have set USGS Color Aerials - Small Tiles to use the services from the National Map Viewer.
Therefore, it should be working when the National Map Viewer is showing imagery, right? Yes, but several times in the last few days, the imagery in the national map viewer hasn't been working. They may be still working out some kinks.
USGS Color Aerials -large tiles - is directly using the US NAIP web service, as before. Most prefer the small tiles, because the proportions match better with Google Maps and other maps you've used.
If it is working, but you have blank or bad data from before, consider using this procedure to clean up old tiles. .
We will continue to monitor the situation to see if the USGS servers will stabilize.
At this time, it appears that MapQuest Open Aerial is having some inconsistencies as well. Their source data is the same, so they could be influenced by what is happening at USGS. At present, they only seem reliable up to zoom level 15.