The colour codes of hydraulic systems referred to, common for 1960's-1970's British Jets, and since then all Airbus aircraft, do not refer to the colour of the fluid!
It is just an identification system for each separate hydraulic branch, the fluids themselves have nothing to do with 'green, yellow, blue' system identifications.
It should also be noted that the American convention is not to use colour codes, on Boeings they typically refer to 'left, right and center' systems.
In terms of the fluid itself, the original question mentioned Concorde. Concorde used Chevron M2V 'Oronite' fluid, which is silicate ester and is a light straw colour.
Almost all civilian airliners used one of the main fire-resistant phosphate ester fluids, either Skydrol or Hyjet - phosphate ester is also naturally a light straw colour, but as specified it is artificially dyed purple for identification. However, phosphate ester aviation hydraulic fluid changes colour when overheated, getting darker, turning from purple to dark purple to grey, to black in extreme cases - or if it leaks and becomes oxidised it turns back to the normal straw yellow colour.
Final mention is for many business jets(Gulfstreams and Citation X excepted) and military aircraft, they use 'red oil' hydraulic fluids, either Mil-5606, 87257 or 83282. They again are probably a straw colour to begin with, but are artificially dyed red per their relevant specifications.
You can generally mix the different red oils, or you can mix the different phosphate esters, but never ever mix red oil and phosphate ester - they have different seal swells etc.
Getting back to the original question: you don't use fluid colour to identify the system, you use the system schematics and the tube/hose identification labels. The colours 'blue/green/yellow' are primarily for illustrative purposes in the pilot operating manual and system descriptions - go to smart cockpit dot com for exmaples.