Flow/Return Colour Codes

[MrGatch]

Are the any standard colour-codes or conventions for labeling central heating, water and gas pipes?

I'm looking at insulating the pipes in my cellar and am considering marking up the flow/return and H/C water pipes as I'm going along.

Appreciate that yellow is for gas and possibly red/blue for hot/cold water, but what about CH flow and return?

 

[Gasmk1]

Hot and cold red and blue obviously, flow and return same but direction denoted with arrows, gas should be yellow ochre but you can just buy tape for all of these applications

 

[Ben-gee]

Use climaflex insulation and just put a ring around of coloured electrical tape every metre or so.
Use different colours for flow return if you like, good idea, just reference it somewhere obvious ie near the boiler.