Keeping it silver

I used to use KMS Color Vitality (Blonde I think) and had a beautiful silver shine to  my grey hair.  Gots lots of compliments and I felt really grand.  My beautician says KMS changed and were not the quality they had been so she quit carrying them.  Have tried several other types of shampoo for gray hair and am now using Simply Sexy Hair Violet Mood.  Sadly, it doesn't do the trick either.

SO---the question is:
What was it in the KMS that I can't seem to find now.  What can I do to get my beautiful silver hair back.  I did not the KMS seemed to be more purple.  While Violet Mood looks almost as dark, it doesn't seem to keep the yellow out.

HELP!!

Hello hope this idea helps you. I had a similar problem but 90% of my yellowing was caused by using the wrong shampoo and conditioner. (sold to me by a hairdresser.) I have beautiful white hair thats been growing out for the past 14 months.

   I tried the silver shampoos and found them to be very drying and the results not lasting. A friend of mine bought me some Tresseme moisturizing shampoo and conditioner with vitamin E. The very first use I noticed my white coming back.  Now I'm on the hunt for some styling products. (I air dry my hair right now.)