It is really easy to do. Make a variable, call it "RNG", then set it to a random number between 1 and x, with x being based on how probable something should occur. Then, make a conditional branch that checks if the variable "RNG" equals 1, 2, 3, ect. Under each of those cases, have the random thing occur. Using your example, it would look something like this:
Control Variables: [0001: RNG] = Random No. 1...3
Conditional Branch: Variable [0001: RNG] == 1
Text: I like blue
Conditional Branch: Variable [0001: RNG] == 2
Text: I like green
Text: I like red
Hope that helps.