If the coin (metal) has begun changing colour due to the effects of the environment / packaging, it is very likely that the coin will be less desirable and therefore worth less.

There are some rare exceptions where toning can look good and increase value – for example rainbow toning may occur in certain conditions on specific coins – but silver 50p coins tend to see light brown toning which make the coin look dirty and is not attractive.

The coin in this picture is the 2019 Stephen Hawking Silver Proof 50p.

You can watch the How to check if your Royal Mint Silver Proof 50p is toning video on the Coin Hunter YouTube channel.

Lift the coin in the capsule out of the presentation box and take it to a window or outside where there is plenty of natural daylight.

Closely inspect both sides, especially the obverse (heads side) as it seems to be more prone to toning. If you have a phone camera that can zoom and focus clearly on parts of the coin - use it to help you inspect the coin, as the first signs of toning can be difficult to see with the naked eye.

The coin shown here (2019 Battle of Hastings from the Celebrating 50 Years of the 50p Military Set) is beginning to tone, it is just possible to see the slight discolouration near to the edge of the coin.

Toning that can just be seen on close inspection with the naked eye, can be seen in great detail and very clearly with a high quality phone camera.

This is the 2019 Heroic Acts Victoria Cross 50p from the same silver proof coin set as the 50p obverse shown in the image above.

You can see the dark brown reaction in the metal edge closest to the black foam material that surrounds the coin.

Whilst coin toning is a natural chemical process that occurs when something reacts with the surface of the metal - if coins are kept in optimal conditions, the process should occur slowly and would normally be seen on coins much older than those dated 2019.