Just jumping in here, but I think fast flashing cyan usually indicates problems with the public server key on the core. Flashing orange (yellow/red) indicates problems with the core-key I believe. If it’s the server public key, then we need to re-write that key to the core.
dfu-util -d 1d50:607f -a 1 -s 0x00001000 -v -D cloud_public.der
You can grab that key here:
https://s3.amazonaws.com/spark-website/cloud_public.der
Instructions for updating private keys here: