He got so far in his investigation!

For the most part you can be creative but for some options:

Ala berry tea This tea is bright purple, but it is very sweet and he will get the feeling it tastes just as good cold as it does hot

Sawn This has a rich earthy taste and will clear his mind somewhat, very refreshing.

Beetlejuice Depending what he knows about Terrans from any communication with Purple team he might not be keen on this one... it's very literal.