"Dummy" ordnance comes in different types.
There is inert, drill, training and trials.
The inert is usually, but not always, a shape. Drill is not usually, but sometimes is, flown and is usually complete so that it can be taken apart and reassembled but no explosive. Training is usually flown and may have working gubbins so that the integration with the weapons system is possible. Finally trials has everything fitted with explosives replaced with an inert ballast and propulsion likewise although that might be 'live' if it was a firing trials round.
Colour also gives a clue but the colour goes with the round and not a universal standard as we keep changing the rules.
The short answer is don't touch and you mate should really tell the police who, in turn, will call out EOD to remove said object. Make sure that they get his name as there may be a reward.
If his is a member of the armed forces then get someone else to discover it. Members of the armed forces have a DUTY to report it and therefore would get no reward.