Factory finishes are often different to Phoenix / Railmatch paint of the same description. If you careful in the renumbering then slight weathering should be enough to hide any imperfections, otherwise its probably a case of mixing paints together to get an exact match. What would be ideal would be model shops with an enamel or modelling acrylic mixing machine that matches a sample you give it like the diy store paint mixers. Sometimes a standard paint can be perfect - Tamiya japenese army green for example has often been quoted for touching up Airfix GWR locos