There is a very big difference between Even money chances at the races & the odds offered at the casino. In the first case Even money chances at the races are only ever an opinion price, even after the race has been run, in reality it could have been a 1/2 chance or a 2/1 chance - it will never be known as it's a buyer's market & over the long term the buyers tend to get it approximately right - it's only the vig that stops many of them winning.

With the casino there is no opinion on the maths that never change on odds/evens; black/red chances, it is always in the negative.