Xantias (and earlier hydro-pneumatic Citroëns) use a special mineral-base hydraulic fluid/oil, Liquide Hydraulique Minerale, or LHM for short.
New LHM is a transparent pale bright green colour like the Delphi LHM+ in the jug (top photo). With age, LHM progressively turns pale greenish yellow, golden (centre photo), yellow (like brake fluid) and eventually dirty yellow-brown (after far too many years in the brake lines).
This often leads Xantia owners to worry that, in the past, something other than LHM has been put in the hydraulic reservoir; usually not because there's any real reason to think the wrong fluid has been used, but simply because the fluid in the reservoir is more gold (middle photo) than green, or yellow, or the fluid bled from the brakes is a dirty yellow-brown, or because a jar of dirty LHM held up to a bright light always looks red (bottom photo) due to the same effect that produces a red sunset. But that's not to say that on occasion, ATF, ordinary brake fluid, or something else hasn't been used to top up a Xantia's hydraulics.
It seems that LHM is formulated to change colour as an indication that it needs changing due to either oxidation or water absorbed from the atmosphere.
It should be remembered that although the LHM circulates through the suspension and the steering hydraulics, the brake lines from the Doseur valve (the equivalent in a Xantia of ordinary cars' brake master cylinder) to the callipers are dead-ends. As the LHM in these lines can only get flushed out by the brakes being bled and the fact that Xantia rear brake pads wear very slowly indeed, if the rear brakes are not bled to flush the lines every few years, the LHM in the rear callipers will be very old and brown!
The pictures at right were taken when doing a full sphere & LHM change; the middle picture is while syphoning out the contents of the reservoir. The bottom picture is of a sample from the can of waste LHM (reservoir contents plus the dirty LHM from purging the brake lines by bleeding); on a sunless day, an LED inspection torch was needed to provide a bright enough white light.