There are two LEDs on the Core. The big fat one in the middle is a full-color RGB LED that shows you the status of the Core’s internet connection. The other small blue LED is the user LED; it’s hooked up to D7, so when you turn the D7 pin HIGH or LOW, it turns on and off, respectively.
The RGB LED could show the following states:
Flashing blue: Listening mode, waiting for network information.
Solid blue: Smart Config complete, network information found.
Flashing green: Connecting to local Wi-Fi network.
Flashing cyan: Connecting to Spark Cloud.
High-speed flashing cyan: Spark Cloud handshake.
Slow breathing cyan: Successfully connected to Spark Cloud.
Flashing yellow: Bootloader mode, waiting for new code via USB or JTAG.
White pulse: Start-up, the Core was powered on or reset.
Flashing white: Factory Reset initiated.
Solid white: Factory Reset complete; rebooting.
Flashing magenta: Updating firmware.
Solid magenta: May have lost connection to the Spark Cloud. Pressing the Reset (RST) button will attempt the update again.
The RGB LED can also let you know if there were errors in establishing an internet connection. A red LED means an error has occurred. These errors might include:
Two red flashes: Connection failure due to bad internet connection. Check your network connection.
Three red flashes: The Cloud is inaccessible, but the internet connection is fine. Check our Twitter feed to see if there have been any reported outages; if not, visit our support page for help.
Four red flashes: The Cloud was reached but the secure handshake failed. Visit our support page for help.
Flashing yellow/red: Bad credentials for the Spark Cloud. Contact the Spark team (email@example.com).
I just had an issue with my Spark flashing Yellow/Red. I checked all other systems that we were asked to check in the troubleshooting section, and there were no problems there. I realized, that since I’m not powered to a USB source, just battery pack, the power was dying. Technically, it was having issues connecting to wifi, but the root cause was the battery source. Just throwing this out there because I think, “Check if power supply is adequate” should be added to the checklist on the troubleshooting page.
As I understand it, he is talking about the blue onboard LED connected to D7.
And answering this - although this is not the topic of this thread ;-): “No, there is no way to do this during deep sleep - but there is also no need to switch it off during deep sleep, since it gets switched off anyhow at the very moment the Core enters deep sleep (unless of course, you added some external circuitry that keeps it lit independent of the Cores state ;-))”
Thank you @ScruffR. I personally liked the brief list of every color and what they mean. In the past when I looked at the “modes” section I would find that I was getting a color pattern that was not listed. It is possible that the list is better, but I still think the first thing on it should be a short table (of contents) that lists the color pattern and the name of the header that is related.