"Lahore indigo" (lahor çividi) again
yes, I guess that's it ... had no time to look up the English term for it. And yes, it can be (and is) used with other colours as well. Being no marbler and only theoretically acquainted with ebru, I wouldn't know about ratio, you'd have to ask a specialist.
Anyway it may well be that the cividi that's sold in darkish lumps in the Istanbul bazaar reacts totally different from what is being sold in little bags for laundry, so be aware.