Effect of boil strength on wort darkening

[ebbytempura]

I've just recently brewed another dark beer recipe and I noticed that when there's isn't a strong enough boil I seem to get less brown flavors and the wort color is lighter by a few degrees than expected.

Am I just imagining this? Is wort darkening very significantly affected between a rolling boil and a lazy boil? Would appreciate any comments on this.