Since when have warnings been green anyway.When warnings go off the master warning sounds depending upon the seriousness of the fault ie fire etc.The bloke must have been a wally if the master warning goes off and he thinks there's a green message and the problem is normal.
The only problem colour blind people might have is on system pages where valves etc are in disagreement I agree you may have problems but there is always someone around to ask colour if needed(pilot,cleaners other eng etc).