Does your blonde get brassy?

It's been almost 7 months since my last highlight and my blonde is really starting to lose it's luster. My natural color is about a medium blonde, so fortunately for me (and my checking account), I'm able to wait this long between highlights. However, my natural color is certainly not as platinum as it used to be. Meet platinum me:
What I would give for hair that blonde. Sigh.

For a period of time during my senior year of high school, I started using ARTec White Violet Shampoo, which claimed to neutralize yellow and maintain brightness of pale blonde highlighted hair. I swear to you, every time I used the shampoo at least one person would ask me, "Did you just dye your hair?" I didn't really notice, but others always did. The ARTec was awesome in terms of getting rid of the brassiness that builds up on blondes overtime.

It dawned on me I should start using it again (not sure why I ever stopped), so off I went to Ulta to purchase this miracle in a bottle. I was scouring the hair care aisle when sadly I found out that they no longer carry it. Womp, womp. (After all, I guess that was 8 years ago.) I was able to find it online, but when I get it in my head that "I have to have it", I want it now.

A sales woman at Ulta recommended AG Hair Cosmetic's Sterling Silver Toning Shampoo:

The lady said it does the same exact thing as the ARTec. I side-eyed her and said, "Are you sure?" She promised me it would and added, "It's on sale for 12.99." Normally $36, I couldn't really pass this deal up. On top of the price slash, I had an Ulta $3.50 off any $10 purchase coupon, so my grand total for the 33.8 oz bottle was less than $10 before tax. Not bad.

It is yet to be known if this stuff actually works, but all the reviews online seem to be positive. I'll have to let you know how I like it after a couple washes. Wish me luck!