The casino offers odds of 49% that either red or black will double your money. That also means the odds of losing are 51%.
It would be great if the odds were that high but it depends if you're playing American or European roulette. An American roulette wheel has a zero, a double-zero and 36 regular numbers so the probability of red or black coming up is 46.37% because all outside bets are lost if zero or double-zero come up. European roulette doesn't have a "00" so the probability of hitting red or black is increased to 48.6%.