brown/black hair dye with ash or not?

i recently had a hair color opps when i went to dye my dark blonde hair brown and it turned black, which i posted message on what to do to fix it.  a few people suggested trying to dye it light brown and hope to get a change.  i went to the store and got clairol ultress in light brown and im planning on trying it (it was only $2- worth a try).  but at this point its been about 3 weeks since my hair turned black and now its looking a little more like a dark brown but reddish in certain lights and my dark blonde roots are growning in a bit.  im not sure if i should go exchange it for a light ash brown or stick with what i have.  ive had my hair turn greenish and greyish before when i apply an ash color but i also have had it turn out very reddish with a regular color...  so obviously i dont quite know what to do.  if anyone has any suggestions please let me know :)