just to throw a bit of math out there, using game theory, we can see that if we take x flips (assuming roulette is a flip, obv it isn't bit the math is alot simpler if we assume this), then the average winning streak of a certain colour will be log2(x) - if we take into account non co-operative game theory we would actually need to calculate the streak vs various run variables but lets forget that as well...
so, assume we're going to pick red 100 times, lets do some math
log2(1) = 0
log2(2) = 1
log2(3) = 1.584962500721156
log2(4) = 2
log2(5) = 2.321928094887362
log2(6) = 2.584962500721156
log2(7) = 2.807354922057604
log2(8) = 3
log2(9) = 3.169925001442312
log2(10) = 3.321928094887362
Note that log2(x) is defined for any x greater than zero. If you have a calculator than computes the natural logarithm (often denoted ln), then you can calculate log2(x) = ln(x)/ln(2). The same thing works with log base 10, i.e. log2(x) = log10(x)/log10(2).
log2(100) is about 6.643856.
For curiousity, if you wanted to write a algorithm to 'guess' a number from 1-100 using a divisor strategy, the average number of guesses required is log2(100) if you use a halving strategy to bracket the answer.
for the graph lovers, a basic log2 giraphe

so for 100 spins of roulette, we can see that a run of 7 black in a row would be well within standard deviation. assuming a $1 base unit bet on a standard martingale system with no bias, we can see that a run where we are down 7 martingale betting units (MBU) would be standard (which is -$64, and needs a bet of $129 for the 8th MBU).
we can actually use the log2(x) to determine the average large bet which will be required to operate the martingale system as well, using MBU = 2^(y-1), where y = log2(x) and x is the expected number of bets.
so, lets say u wanted to go pro at roulette. you work an 8 hour day, during which time i'm guessing we could expect 50 spins an hour (assuming only you on the table, it's a simple bet to pay, also assuming there is no house limit on the max bet, the formula above actually lets u work out what tables u can 'profitably' play using martingale with the number of spins you wish to play as your input variable)
so were going to see 400 spins/day, and log2(400) is approx 8.64 so lets round that up to 9. we can see that using martingale aproach, we can expect to have 9 spin losing streaks as an average, or 256 MBU.therefore, assuming a $1 base bet, as long as the table max was less than this, you could argue that a martingale system would be 'profitable' on this table. however, i've never seen a roulette table where the table max was 256x the table min (it's almost like the casino's have sat down and done the math as well
)
anyway, it's hot, i'm going to get a soda,
alc out