I had the same exact color in some parts. The lighter parts ended up toned nice and that orangy type of color turned yellowish. If you just recently applied bleach, let your hair rest before re-bleaching it. Or I suggest you use some other toner first, something that will remove orange color from your hair and only use t18 after that. I wanted to dye my hair silver afterwards, so my results were not really good. :/
In short, no it's not. You do need to lighten it further with a bleach bath.
But t18 isn't the best thing if you don't want to cause more damage. Silver shampoo is much better for your hair. Also violet dye mixed with conditioner.