Please help!! Orange + purple hair!!

Since you are wanting your roots lighter, and your hair darker, it is complicated.  You really may want to consider letting a pro handle it.  I will explain:

That's why I sort of dislike blue bases.  Its harder to find green bases on blonde shades these days, but those went orange a lot less than the blue does.  Blue bases won't get rid of brassiness when you are going blonde.  They will help counteract the orange that comes out in the hair (though not as well as green would), but the hair will indeed wind up gold, and need something else (violet base) to make it less brassy/yellow.  I'm not a pro but I have this same problem using blue based dye to do my roots for my blonde highlights....and the next time I go shopping for blonde dye, I'm looking harder for a green based one!

If your hair is that much darker than the color you are dying it to, root upkeep is always going to be a bit of a challenge.  Not only to get it to match, but to make sure there are no bands in it of uneven color.  You will have to be prepared to maybe have to mess with it more than once.  It will be best to do your roots and get them lifted past the orange stage before doing anything to your length.  You don't really want to use a blue base on already blonde hair, it won't do anything good.  Only use violet for making it less yellow if you need anything at all...definitely don't use blue then blue/violet, that's a double punch and really too much.   

I'm so glad you test stranded before doing your whole head!  So many people don't do it, but it really saves you a world of hurt!    By using 20 volume developer on your roots, you are making them take a lot longer, 30 will get past orange quicker, but you will have to test strand and time it carefully.

Now, about going darker, that is a whole different ballgame.  If your hair is pretty white, its going to be a big challenge to do your whole head because your base color will always show through (very badly) and you may have to do it more than once to get it darker.  Then it will wash out quickly too because your hair is very porous (even if its permanent).  If you don't want to go much darker, and your hair is more yellow than white, use a violet base, test strand and get the timing right.  10 volume developer should be enough for that since you don't want to go lighter. 

I haven't tried unred.  I did like green better because it seemed to counter the orange more thoroughly and my hair came out a little less brassy when it was finished.  Sometimes greens can leave a faint green tint when you go blonde (especially if they are overdone, like if the green is used when the hair is past the orange stage) but its really a very faint tint and does wash out after a week or so (so green does have a bad side, but at least to me, thats not as bad as the brassy yellow hair I get from the blue that I have to mess with again). 

I'm glad it worked out, if you don't want to mess with the gold roots, you can try doing a roots only wash with a pigment shampoo like Complements which can be bought at Sally.  (Not the color enhancing shampoos like you can get anywhere, but the pigment ones that look like paint in the bottle).  I have the ash brown one and it counters yellow pretty well.  That's what the violet one is for, but I haven't tried that and I'm afraid it may leave purple on the parts of your hair that aren't very yellow.  You can wash your hair with your normal shampoo, rinse it out, then use the ash brown on your roots only.  Then condition with your usual only from the ears down, not the roots.  It won't turn your hair brown at all if you only use it once and wash it out with normal shampoo for each first wash, but it will help tone down the yellow very slightly so you might like it better.