Rosemary (the essential oil) is supposed to be good for hair; however, I do not believe it lightens it.

Probably a few drops added to a bottle of shampoo would be enough.

Lemon juice is also good for giving blonde/light brown hair highlights. Put some lemon juice and water into a spray bottle, spritz onto your hair and go into the sun for a little bit. In fact, you can make a chamomile tea, add lemon juice and spritz on.

Rosemary is a wonderful herb for dark hair - makes it shiny and manageable. It is usually recommended for dark hair and chamomile (and lemon) for fair hair, but I cannot see that it could hurt fair hair... it does not darken hair as a strong infusion of sage is reputed to do...

My hair used to be very dark brown (LOL - quite a few years ago!) and rosemary tea made it shine! BTW, have you ever tried an egg shampoo? Messy, but excellent!

To generalize broadly about harmless plants, lighter ones intensify lighter highlights, and darker ones intesfy darker highlights.

I have found that even natural astringents can aggrivate the hair into producing extra oils, while some moisturizers displace natural moistness.

Let me also suggest that, no matter how you try to wash them out, things which dry opaquely or attract dust will do the opposite of clarifying.

Another thing to consider is henna.
It comes in a wide variety of shades, and won't lighten your hair, but gives it a color boost.
Plus, it seals the shaft once it's plumped up with water, so your hair feels really thick and smooth. I occassionally use the neutral henna which doesn't affect the color but does give you that nice shine and fullness.

Where do you find henna?

Most health food stores sell it these days. And I'm sure there are a million places on-line where you can order it.

Back in the day, I used to get the powder, and mix it up into a paste. It could be messy, and it wasn't always easy to comb it evenly thru your hair. But these days you can buy it pre-mixed and it's much easier to use.