Whoa whoa whoa, unless I missed something here, there is no such thing as "improving" the odds in roulette. It's either going to hit 0/00/red/black. One spin has no influence on the next.
Okay, let me say it another way. The odds of 21 Reds in a row (before the 1st Red in the streak has been spun) is 0.0000268%. The odds of the 21st Red in the 21 streak being spun after 20 Reds have already been spun is 48.65%. The 21 streak being completed is more likely after the first 20 Reds have already been spun.