Pthalo Blue

That'th my boy, Thyd! Dilute it, use it wet in wet, don't be intimidated by it - I expect you know the work of Arnold Lowry, a kid who is somewhere between your age and mine? If you look him up on YouTube, you'll find painting demos in which he uses all sorts of powerful colours: his secret (though he shares it freely) is to use them on a "living", ie wet, paper - he says that when the paper's wet, it's alive, when it's dry it's dead. Now - I know there are other ways of looking at this - Alan Owen, one of my favourite watercolourists, uses wet on dry very often and does so extremely successfully: he achieves beautifully pale washes which I just can't get on the paper I'm using at the moment. Alan also uses Winsor Blue now and then, but then he has 60 plus years of experience in watercolour, whereas I suppose I've been painting with it for less than 20. Even I can make Pthalo Blue work for me, though, IF I keep the paper wet, and sometimes tone it down with Cad Red. I'm less confident with Prussian Blue, but I would suggest you try the Pthalo: ensuring only that you make it a good one: I'm convinced that some brands of PB are weaker and cruder than others, and suspect that this goes for other hues as well (in fact, I'm sure it does, but that's a longer story, and not restricted to watercolour).