Hi Ellen, my hair is very similar to yours, a bit bitty really! I have areas of white, then patches of my natural very dark brown & strangely a few bits of brassy blonde (where did that spring from!)
Anyway, a hairdresser suggested that an ash blonde colour would suit me as I have pale olive skin but it just seems so blurgh & dull! I have brough a couple of different shades but I might try a light brown with a few subtle blonde highlights or wear a hat; as I have often done after a bodged-up hairdresser debacle!
Oh, not much difference between semi-perminent or permanent; roots appear regardless but semi's can be a little cheaper on the main.
Anyway, lf it all goes wrong, just smile & wave, smile & wave... then have a little cry. 🙂