How to apply filter to one specific grid gallery on 7.0 site without affecting other pages?

Site URL: https://animausa.com/buckythebucktooth

I have a site where I have grid gallery images on my pages, and I'm trying to code it where the grid gallery under the "merch" section is greyed out. Only the specific grid gallery images under the "merch" section, not the other gallery images. How would I go about doing this? The website is animausa.com/buckythebucktooth

It looks like you solved with this CSS?

#block-yui_3_17_2_1_1576010676806_27377 {
    filter: grayscale(100%);
}