show custom field in slider query string

I have a custom field as a dropdown select with four options in it, say: red,blue,yellow,white
I want to make four separate sliders for these on the home page, so slider one displays only those where red is selected, slider 2 displays blue.

Ive tried every combination I can think of

what do I add to this to select from my customfield only, with example database name= xyz

meta_key=frontpage&meta_value=yes

I really need this query string