I'm sure I have enough fabric now to make one for my son, a 43 year old who does not want a "girley" type couch throw.
Like your FIL, he wants a masculine one. So I'm going with black, white and gray, with 4 corner stones with applique of our beloved Yosemite Valley's Fire Fall he watched with such wonder as a child. That will be the only color in it. The rest will be a "Floating" mass of different patterned rectangles with stark black floaters, medium gray background. Saw one like it on this forum and was entranced with it. Sure wish I could find where I put a picture of it that I copied and pasted!
Might think of something like that for your nice FIL. Good to hear you have such a nice one you want to do such a labor of love for. Cherish him and your nice MIL too.