The Grey waterline is polybutylene. The fittings used are barbed grey with either aluminum or copper crimp bands .as long as your waterlines are not developing pin holes in the tubing itself you can replace all of the fittings with flair-it brand  or sharkbite. flair-it being the cheaper can be obtained from a Mfg Housing parts store in you area sharkbites at local building supply house. If you want or must replace tubeing polyethelene(PEX) is the replacement same stores will carry this. Hope this helps