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"Haemosiderin staining" describes orange/red/brown skin hyperpigmentation caused by haemosiderin (an iron-containing pigment found in blood) leaking into the skin.
Causes:
Chronic venous insufficiency (in lower legs)
Skin inflammation
Trauma e.g. wound, fracture, surgery
Pigmented purpuric dermatoses
Haemochromatosis
Haemosiderin staining may be exacerbated by anticoagulant use as this increases extravasation (leakage) of red blood cells into the skin.
See an example here.