A quick note: home shrines aren’t called altars – altars are reserved for churches and places where Mass is licitly altered. Many threads have been derailed because of this term.
Now that that’s out of the way, after reading the link that Joannm provided, I didn’t get the sense that home shrines shold be covered unless it’s the custom…since home shrines are private devotions and not regulated by the CCL, there should be no problem in an individual’s preference or choice to cover or not cover.
My Babka would cover her shrines with a small purple cloth. I don’t cover my statues, but have sewn mantles and capes (for our Lady of LaVang statue and the Infant of Prague) in violet to reflect the Liturgical Season.