Never allow your piece to be in direct sunlight. Although I only use professional materials, which are lightfast, the only way to maintain the original colours of the piece for decades is to protect it from sunlight. Protect the piece with museum glass which is acid free e protects from UV rays. This is more expensive, but it will maintain the original colours for decades. The matt should also be acid free.

Make sure the piece is protected from humidity and other hazards that will damage the paper. Again, I only use high quality materials, but no paper is safe from a blade!! If you ever decide to change the matt or the frame, for instance, it is best to let it be done by professionals.