fuel line return fuel out ie to injectors at pump&sender

[bambi mk 1]

You will blow back through the return a hell of a lot easier than the feed with a pump attached to it

[Bush Mechanic]

I realise this is an old thread but in the interests of those who've stumbled across this thread it in their search for answers, here's what the Ford workshop manual has to say on the subject.

SECT 310-00-19
15. NOTE:Fuel supply line connectors are white
or are identified by a white band. Fuel
return line connectors are red or are
identified by a red band.

Hope this helps.