Are online roulette tricks legal?
Depends on what you mean by tricks. Online roulette is powered by an RNG (a random number generator algorithm), which makes any bias analysis pretty much useless. All that you have left are betting strategies, which are all allowed and legal.
If by tricks you mean any sort of hacking or manipulation of the software, then no, it’s not allowed. At best, you’d be banned from the casino; at worst, you’ll be prosecuted.