737 Manual Pressurizaton Green Light?

[None]

Why would Boeing decide that when the 737 pressurization mode selector is in Manual that green is the best color for the "MANUAL" light?

Takeoff with manual pressurization would normally be considered an abnormal event. Wouldn't that warrant an amber (if not red) light?

[Skyjob]

Before using the Manual Pressurisation Mode Selector, you'd have other AMBER light is already illuminated.
AUTO FAIL

If alternate system works fine, ALTN is GREEN, otherwise extinguished.

A change of colour to indicate best what control you do have is normal human behaviour, many amber lights indicate failed states, thus green indicates what works.
Same philosophy goes for MANUAL, if it works its GREEN

[Centaurus]

Takeoff with manual pressurization would normally be considered an abnormal event

Abnormal? Not with one (unnamed) Indonesian 737 Classic operator who frequently dispatches in Manual Pressurisation as normal event because of lack of maintenance. Six emergency descents in as many weeks.