Thanks for that information. I got colourify and colourize mixed up; They both do similar things differently.
About the luminosity, I got it confused with lightness, which is what the L in the HSL for colourize stands for. Lightness confuses me because it goes into negative values, essentially making it a slider that goes from 0 to 200, similarly to Channel Mixer.
Either way it all worked out and I am too lazy to fix the final result, but thanks for mentioning the brushes. Even though I mention in attribution, I say "No attribution required" because... well, none is required if the author states so. But I like to be awfully specific when it comes to this stuff and give credit even when it isn't due because man do they deserve it.
Not to guilt-trip, post away and keep your stuff hidden if it's your own secret sauce but it's still awesome to know these things so somebody might come along this thread and make it better to their own preference. Thanks again for the art, XCF and information.