2023—Keynote 13.0—how to change background texture's color?

I'm trying to change the color of the background linen texture on Keynote Master Slides from olive green to the dusty blue seen here: I was able to change the background color on the ***plain*** slides, as seen in that image, but am not able to change the edges on slides built of several layers (by Apple) to simulate a book page. I have gone into **Applications>Keynote.app>Contents>Resources** to look at the assets and found some useful items *(i.e., canvas_bluepurple_low_res.jpg, canvas_bluepurple_mipmaps.plist, canvas_bluepurple_jpg, Linen.sfcimage.plist, Linen.sfctex.plist, tile_bluepurple.jpg)* but don't see how to use them to change the theme color for ALL the slide masters. I know this has been asked before (https://bit.ly/3KqLVI2) but responders didn't seem to understand the OP's question. I hope the image I've shared above—showing the green tint to the linen frame around the slide (making it look like a linen-covered book) and the blue-purple color I was able to use as a background for the Title Slide—will help clarify.