I was originally a dark strawberry blonde. (had henna in my hair for years and a few months ago began lightening it) Last night I used a (i think it was loreal preference?) hair dye meant to turn dark hair to blonde. Now my head is a light orange! Now this has kind of happened before.. I bleached my bright red hair a long time ago and bright orange was the result. I used ash blonde dye to counteract it and it worked in fixing it but it turned out an ash brown. Should I do this again? The only issue is the goal that I wanted was to have a natural looking blonde hair with lavender highlights. How can I get a natural blonde from this? And soon! As in like today, not over time... Also don't suggest going to a hair dresser because it's not going to happen.
The thing is, though we won't tell you to go to a hairdresser (most of use don't) we also won't advise using anything that will lighten your hair today. The reason for this is that you should never use two permanent hair dyes (dyes with peroxide and very strong peroxide in the case of most blonde dyes) more than once in a month. You run the risk of very badly, maybe irreversibly, damaging your hair.
At the moment, the only thing I can suggest, if it HAS to be today, is to either get a blue dye which you can dilute with conditioner to neutralize the orange to a light brown. Or, get an ash brown semi dye which is a little darker than what you have now.
You could try a colour remover, but I highly doubt it'll work on hennaed hair.
I'm totally aware this isn't what you want to hear, but I can't suggest anything else.
I agree with Janine. If you want your hair in good condition, it will have to be a slow process. Henna is extremely difficult to remove from the hair and since you bleached last night ( blonde dyes for dark hair are just bleach with a bit of color) then i wouldnt suggest doing it again for at least 4 weeks.
Covering it up with a semi dye is your best choice for now.