So we have Bronze, Silver and Gold for talismans so far. This is one suggestion I have for another level of difficulty: platinum or diamond, which is a light-blue disc (around the region of RGB 0, 255, 255).
The reason for this one is because some of the talisman suggestions that are coming in for Revenge of the Lemmings are beyond difficult, like "The Floodgates Open - complete in under 3 minutes." would be so much harder than the other Gold-level talismans. Either that or the pack creators should just re-scale their difficulty ratings a bit more.
Not sure if it's worth it or not, but it would be nice to have the option.