The lids colours depict what size and type opening there is to put your sharps through..
I know some councils/area's use a different sharp coloured box dependant to who it's being given too, with normal medical conditions getting the yellow, and drug addicts who's using a needle exchange system being given grey!
Cytotoxic drugs have to be returned to the hospital can't be put in a sharps bin.. residental/nursing homes will have a hospital number to phone for collection
Controlled drugs, have to be disposed of in a special container that has liquid that dissolves the drug, then sent back to the pharmcy
Other none used drugs, just need to be suitable stored in marked container returned to the pharmcy..
They did used to do a special container for medication but now as above