Ok, the chance of loosing to 4 cards of same colour is (assuming 6 deck game):
1*155/311*154/310*153/309 = 12.26%.
Average value of a hand in blackjack is 49.5%, but since a blackjack pays 1:1, that lowers it by about 2.5% to 47%. The chance of winning at least one hand is 1-(0.47^2) = 77.9%.
so you have
12.26% will loose 1
32.1% will loose 1
77.9% will win 1, if you pick the right hand, else loose.
Standard deviation in blackjack is 1.3 and 1.4 for two hands. Meaning if you take the best hand, you will still only be correct 10% of the time more than you are incorrect. so about 77.9/2 -5 = 33.95% you pick the wrong hand, and 43.95 you pick the right hand.
So all up I would say you win 1:1 43.95% of the time and loose 1:1 the rest of the time, for a house edge of about 12.1%
this is a rough guesstimate only.
Obviously high counts would amplifty the rate at which the house edge favour you though. It would be interesting to see when it becomes profitable to bet. Only have to have 1 hand hit a 18/19/20 to win would be awesome.