白い雲

Flying in a blue dream is Lydian, so you could experiment with that for the ethereal sound. Glasgow Kiss is Mixolydian. As for conveying something dangerous sounding, have you heard "Race with Devil on Spanish Highway" by Al DiMeola? To me, that song conveys that feeling. That uses Phrygian. The harmony of a song plays a big role in the sound too. I like to analyze chord progressions in songs to get an idea of how the mood is created, and look for patterns between songs.

Now, here are some more general suggestions:

Learn/experiment with different scales, try out different chord progressions, try out different types of chord alterations. You can actually use a melody you already have, and reharmonize it in different modes and chord progressions to see what sound fits for you.

Analyze the melody, arrangemet, and harmony of songs you like, to get an idea of how they convey the emotion they do.

You might need to learn more theory to understand some of the things you're trying to do or some of the songs you analyze. Teachers are the best bet of course, and books are good too. "Tonal Harmony" by Kostka and Payne is good for basic theory, "The Jazz Theory Book" by Mark Levine is good for the more 20th century tonal music ideas used not only in jazz, but also rock, classical music, and pop. One book that you might find very beneficial is "Jazz Composition: Theory and Practice" by Ted Pease. I also like Tom Kolb's books, "Chord Progressions for Guitar" and "Soloing Strategies for Guitar". He's also got a book on modes, and one on theory, but I haven't read them, so I can't attest to them.

Now, that's enough to give you a proper headache! Perhaps even more important than any of the above is to try to create and develop sounds that are purely from your own imagination. People do this with melodies, sure, but try it with chord progressions too. When I do this, I'll usually write out the roots of the chords I hear in my head first, and then experiment with voicings and chord constructions until I find what I'm looking for. It can help a lot to put stuff into a program that'll play them back, so that you can hear what you wrote easily. Cheers!

p.s. when I said teachers are good, I meant good teachers are good . Unfortunately, there are a lot of teachers out there who are good at teaching your basic rock guitar and blues or pop songwriting, but not much else. If you ask a question about a more complex topic and your teacher tries to convince you that it's unnecessary complicated, or a fringe idea that's not worth learning, then maybe look elsewhere.