Dark seaweed-colored hair dye?

[Trade Winds]

Where can I find a relatively dark, seaweed-ish hair dye (or maybe somehow combine colors or not bleach my hair to obtain the look)? I was looking at Manic Panic's Venus Envy, but I'd like something darker. I love the idea of looking like I have seaweed in my hair. The plan is to do just a couple strips. I have a green hair extension, but frankly I can't put it in to save my life and would like to dye! I have very dark brown hair and have never dyed it tho, so I also have no clue what I'm doing (which is what friends are for).

I'm not sure how to describe the color I'm going for, aside from darker than what I can find online, and with a brown-green tinge. Kinda like the mermaid tail in my profile pic, but not as dark.

[Aziara]

If you do a medium green dye over unbleached dark brown hair, it should come out as a very dark green. I used the green envy from manic panic, and it was deep hunter green. Keep in mind that oddly colored dyes usually work more as a overlay of color rather than totally coloring, so the color of your own hair will affect the finished color.

[Mermaid Waverly]

i like the "Ion" brand ( you can pick it up at sallys beauty supply) they have a Teal that is absolutely beautiful! I scooped up 5 boxes when they were on sale. but mix equal parts color with 30 or 40 vol. developer ( depending on how dark your hair is) and vola! non-bleached hair!

i change my hair color as often as i change my mind lol