Other than colour , you can identify the oil by its odour (smell).
In case its engine oil leaking from the crank seal it is not a big threat as it will not ruin your clutch plate coz its behind the flywheel.
But, if its gear oil leaking from main clutch drive shaft then it can mess up your clutch plate so in this case you should hurry fixing it.
Do ensure that both the axle seals in the gear box and oil chamber seal is not leaking before getting in to dismantling engine and transaxle.