The NDO is a volume-based indicator that indicates how many standard deviations the volume is away from the mean volume.
In other words, this script is useful for detecting when the volume is abnormally large, spotting pumps and dumps, and movement of whales.
Green indicates that the volume is more than 3 standard devs away from the mean, yellow means its more than 2 standard deviations away from the mean, and orange means it is more than 1 standard deviation away from the mean, with red means volume is less than one standard deviation from the mean.
Statistically, 68% of results show up in 1 standard deviations of the mean, 95% in 2 standard deviations of the mean, 99.7% in 3 standard deviations of the mean, making green highly abnormal.