A previous question here says that Champagne has a blue/violet base and Lavender Ice has a violet base. So Lavender Ice is bets for yellow hair, and Champagne is best for hair that pulls a lot of orange.

Silver is light but same violet tones.....fade the hair with dandruff shampoo and vitamin c to get back to your pale blonde hair....if it doesn't work use a mild bleach batch with 10 volume .....watch closely......to fade color....then use neutral porosity treatment.....then use ION  titanium or try roux rinse in silver lining or true steel .....must gentler and can be mixed to customize color .....you can always go Semi if more perm results needed

10vol to deposit and 20 to lift and deposit 

Copper = red/orange so you need green/blue......teal almost ....try Ion brights in teal ....mix 1/4 tube with 2 cups white conditioner....if already color treated use neutral porosity treatment first like a good primer before the color ....or you good use level 7 or 6 Demi...if you want to diminish the orangy use blue base if the reddish use green base....or mix two ....you can customize it ....always prime with neutral FIRST 

Highlights can be made just using a Demi on the gray hair......2 - 3 shades lighter than non gray hair.....looks natural .....much easier than lifting non gray hair .....easier solution.....advanced gray solution by Clairol .....6light golden chestnut would look good on level 5-3 hair 

Use titanium from ION on brassy ends if orangy yellow .....if reddish you can use shamrock 

It depends on how dark or light you want the blue color to be. You definitely have to lighten with bleach. The secret is to tone your hair before you apply a direct dye. 1. bleach first, 2. tone it to get the yellow/orange out, 3. Apply direct dye Couple of notes on this. Make sure you tone your hair at the right level. For example, T18 is meant for level 9 and above. If you only get your hair to a level 7, then it's a waste of money. You can Google hair level and toner charts to see which one you need. Also, go with a purple based blue color. I've had good luck with Ion's Tanzanite. Clairol's Color Crave in Indigo made my hair have a greenish overcast. If your hair does happen to turn a greenish color, you can always mix a tiny bit of red dye with conditioner and apply it for a couple of minutes in the shower. Honestly, I think you should do highlights (you could pull them through a cap and apply the bleach mid-shaft to ends), tone those pieces, and then put a direct dye (semi-permanant) over all your hair. The highlighted parts will be blue, and the rest of your hair will "shine" a dark blue color in the sun. I think that would be beautiful.

No it will pull out the orange and yellow and balance it out. It might be a bit darker looking than platinum at first but it fades back quickly.