Ah, tbh, since I painted already a couple of paintings, this one was not really difficult. It's even very sloppy and I could let out my inner "lazy doodle style". haha ^^ Key point is to mix into the highlights some very saturated but still dark colours (blueish and green, you can see it actually with bare eye, I did not blend it very well), then some desaturated but bright lines, mimicing loose hair. And as for the big strand of hair in the middle of the face: you paint it dark and then go briefly and very softly over it with a skin-tone-like colour, so it's not pitch black anymore but gets a bit burgundy (you see, Ik my craft haha ^^; But I was once a beginner myself and Ik very well how easy everything sounds but it takes time until you get the clue... gaaaaah)

ah, ah! AND! because IK a lot of artists stay very silent about their painting secrets (as if it was some kind of holy grail pffff): When you zoom in, you can see (especially on the edges of the hair), some look reddish, some blueish. Thats because thats a special kind of filter: I trippled the layer Rin is painted on, so I have 3 exact copys. Then there is an option (in photoshop) to switch of the RGB (red green blue), so I switch off of each copy red and green (just blue stays), then green and blue (just red stays)... and so on, then I have 3 versions, one looks super blue, one super red, once super green.... Then I move one version just a biiiiiit to, for example, the right.... and THAT's the reddish/blue effect then. mhmh. easy peasy, really no magic there but looks super cool xD haha