I've had it for 3 days. It's getting worse by the day. I placed it next to two other orchids, now just moved it away to a different room altogether. Are they in danger too? should I take any preventive action? I will cut the leaves and sprinkle cinnamon right away.
I doubt your others are in any danger, but always better safe than sorry. With such strong roots, hopefully it will recover, but it looked like the crown was already affected.
I'm not sure what that is, but it could be a bacterial rot or something. Definitely could kill the leaves. Maybe someone else will jump in and suggest if a fungicide would help although this looks right thru the tissue of the leaf.
As for the roots, they are bright green like that when wet and then slowly turn silvery grey when they dry out. It's normal and happens every time you water. It's a good indication of when its time to water. Kind of like a gauge! Good luck with it.
Take cotton balls dipped in isopropyl alcohol and wipe down the leaves and main stem of your other orchids to kill any infection that might have gotten on them. If there is anything unaffected by the rot in the afflicted plant, wipe it down with alcohol, too. (roots and flowers are exempt as the alcohol would harm them.) Here are some links that might prove helpful:
These are from orchid societies: