When you say "dark patches", what exactly do you mean- are these like bronxed cheek coloring? or are you talking about brown bloches which resemble pigmentation marks or look like birth-marks?
Both of those are the results of skin damage and they will fade over time- but fact is, the skin itself is damaged and unless you protect it with SPF cream containing both UVA and UVB screens, then the patches will only get worse- you will get more of them and the ones you have will not fade.
To fade the ones you do have, I would see a specialist to see exactly what they really are and what treatment to take, some may advise retinol A which is for ageing skin and only to be used in small doses!