Background: Hair = natural blonde quite fair, I've had a few highlights over the years, think once a year or every 2 years, subtle, so only had it done maybe 6 times in my life.
What happened: Had them done, asked to go a bit blonder as bored. Was OK but subtle colour and a bit stripey around the parting.
So: Went to another hairdresser and said more more blonde please and I'm not keen on this stripey vibe.
Now: Have kind of some super-blonde bits and while it's fine from about 2 inches down (where the old roots were) it's too stripey on top and some is mega white and a bit of an odd colour.
Problem: Not keen and am VERY bored and feeling a bit reckless. Also having just done £££ on 2 different hairdressers I am not keen on going to yet another one!!!
Question: What will happen if I put one of those Boots box nice n easy or whatever things on it? Will that tone the too-light bits down a bit and even it out on the stripey bits? Will it go weird and all fall out? Any other suggestions?
I have never done a box-thing before and am really quite a novice at hair dye / bleaching so am probably making all the mistakes most people make at 20. I am however 40 
Any ideas or warnings? TIA 