I used Nightblooming's Rusalki mix 8 days ago to cover my whites and give my fading natural strawberry blonde a boost. My hair looked amazing albeit a bit bright, but then noticeably faded after washing.
I followed Nightblooming's directions. I used distilled water with chamomile tea bags for the liquid. I only left it in my hair for 45 minutes after application was completed. My test strip was perfect with that timing. AND having used Light Mountain Light Red colour 5 years ago, 45 minutes was too long with that one because I ended up with a too bright, unnatural result.
I used the mermaid method to rinse out and then washed with silicone free conditioner to get all that mud out. My hair felt amazing and looked a bit bright but incredible. I washed with shampoo on day 3 and blow-dried, knowing that it could darken a bit. After washing I noticed many of my whites were completely white again. My lengths were faded and didn't/don't look like I used henna at all. Only parts of my roots have retained some colour.
(I'm in Canada, not sure that part matters... But following rules)