Benchmark: timing 500000 iterations of chromatic, chromatic2, lookbehind...
 chromatic: 18 wallclock secs (18.83 usr + 0.01 sys = 18.84 CPU) @ 26543.50/s
chromatic2: 13 wallclock secs (13.55 usr + 0.00 sys = 13.55 CPU) @ 36900.37/s
lookbehind: 14 wallclock secs (14.95 usr + 0.00 sys = 14.95 CPU) @ 33442.58/s