RYGB
RBYG
GBRY
YRBG
BGYR
https://ibb.co/M2rg3k8How would you compute the probabilities of each colour per position?
From a (somewhat) cursory look, that gives each of these a 25% probability:
BYRG
GRYB
RGBY
YBGR
More interesting is optimizing the best way forward. In general, that depends on what your goal is. typical ones are “minimize expected number of guesses” and “minimize worst-case number of guesses”