All the different pipes/conduits on diesel locos were colour coded for ease of identification, don't know when it was introduced but it was certainly there in the seventies so they were probably built like it the sixties.
There were several colours,
Orange for electrical,
Lube oil was pink
Fuel oil (diesel) was brown
Water was blue
There are a few more that others will probably remember - my MP12 was a long time ago!