Think of it this way:

On 1000 spins of a wheel you will get 500 red and 500 black (assumign no green on roullete wheel).

So if you had 5 red in a row. Lets assume that we always get 500 reds every 1000 spins. So we have 495 more to go in the next 995 spins. Your advantage has now gone to 500/995 for black which is 50.2%

The above assumes that exactly 500/500 comes out for each colour and that there is no green on the wheel. If you include the green then your still at a disadvantage.

Now your talking favourites. They don't have a 50/50 chance. They are closer to 30%. So lets go 1000 races and you had 5 favs in a row lose. That means your expectation is now that 300 will win from 995 bets. Your increased chance has gone from 30% to 30.1%.