Different colours did indeed exist, but I dont believe they bear any relation to the substance they were carrying. Although it didnt always happen I would suspect that if braiding came away from a hose (regardless of where it was fitted) it would generally be replaced, certainly in the case of fuel line for example.
Although black rubber hose would relate to black/yellow used for oxygen, I'd think it was more a coincidence than intentional. I dont know of any gas or liquid that used or uses salmon pink for example, so a salmon pink rubber hose would not relate to any gas that might be carried.
Hoses would be made in a certain way depending on what job they were intended for. So they might be certain thicknesses, or reinforced depending on if they carried a gas of some sort, liquid, were to be used at high or low temperature or under extreme pressure. To make a hose easily identifiable colour coding would be applied, especially if fixed in an aircraft. So a black/yellow hose would immediately be recognised as one carring oxygen, regardless if it was fixed to a mask, or a rigid one fixed in an aircraft.
Years ago I did have a complete colour code chart for pipes and hoses (most being aircraft) but I cant for the life of me recall where it came from or where it went. If I can remember and can find it I'll let you know what it says.