Quick update guys. It may save you some time. I got the Raspberry Pi Zero W rainbow screen today on my first boot. The SD card works ok, tested on my other Zeros. The power has been supplied from the original power adapter (Raspberry Pi) – works on other Zeros but the Raspberry Pi Zero W rainbow screen was still there. I have tried other cards, no luck. Same with the Raspbian Lite vs full version of Raspbian, no luck either my Raspberry Pi Zero W rainbow screen was still there to greet me.
Raspberry Pi Zero W rainbow screen – solution
Fortunately – there are new images available on the www.raspberrypi.org so make sure you will download it! This will solve the issue with the Raspberry Pi Zero W rainbow screen. Sadly swapping the card from an old Raspberry Pi is not always the way to go. Since it’s unlikely that your previous Zero is connected to the internet, you will need another RPI to perform the distro upgrade. The annoying part is that Raspberry Pi Zero W has the internet, but until you update your SD card, you won’t be able to boot.
sudo apt-get dist-upgrade
Otherwise, you are left with good old fashioned – save your work and start from scratch. As usual, always keep your images updated. I have not seen an update on this yet on the internet – I hope this will save you some time. Have fun with your new device!