Buy good quality rattan furniture to avoid the problem of fading
Good quality synthetic rattan garden furniture doesn’t fade as the dye is incorporated throughout the whole weave strand.
Cheap rattan furniture however is only surface dyed so over-exposure to strong sunlight can fade the material; unfortunately there is not a lot you can do to restore it to its original condition. Synthetic rattan is impossible to paint or dye, as you cannot sand down the weave to provide purchase for the paint; if you do succeed in painting with a specialised paint product for plastics it will almost certainly soon begin to peel. The only solution is to place the furniture out of strong sunlight which almost defeats the object of sitting outside in the garden in the sunshine.