you could generate a random number with random() (see https://docs.mendix.com/refguide/mathematical-function-calls) and then use an exclusive split to pick an enumeration value. The random number generation could look like follows:
round(random() * 10).
this should generate a number between 0 and 10 [Disclaimer: I haven't tested that]
E.g. if randomNumber = 0
else if randomNumber = 1
then Enum.Blue etc.