There are 20 versions of Shade keys. These items are all obtained during the Shades of Mort'ton minigame as a reward after cremating a shade. Shade keys come in 4 metals, and 5 colours.
The type of metal from which the key is made directly determines the list of rewards the player can obtain from the chest. For example, bronze keys will generate low level armour and weapons such as steel and black, silver keys will generate higher value items such as rune, adamant, and rarely mithril armour and weapons. There is a long list of items obtainable from each type of chest, including runes, jewellery, clue scrolls, and melee armour and weapons. The colour of a key will not change the natural drops of a key type, for example, a bronze key purple will still only generate low level armour and items, but has a better chance of generating 'good' low level armour.
The colour of the loop of the key determines the probability of generating each reward from its list. Better key colours have a higher chance of generating better rewards, worse key colours have a lower chance of generating better rewards. However, it is important to note that all keys of the same metal type have the exact same reward list. The only thing that changes across key colours is the probability of obtaining better rewards. For example, a silver key purple has a much better chance of generating a rune scimitar then a silver key red, both keys can generate the exact same items. From lower (worst) chance to higher (best) chance: Red, Brown, Crimson, Black, Purple.
Occasionally, after receiving the reward from the chest within the tombs, players will receive a message that they have found a quantity of swamp paste in the bottom of the chest--this is often accompanied by a sum of coins. This seems to occur sporadically but can be expected while redeeming any significant number of keys. Whilst using 75 silver keys of various colour, a player might be expected to earn roughly 27 swamp paste per key. In practice, one key by itself may yield a much smaller amount (or even a greater amount.)