try to think of it this way.
its not so much that they *cant* see it, it just doesnt stand out to them like it does to us.
they can see it loud and clear - just in shades of grey. the color that catches our eye as unnatural doesnt matter in their world.
when you have a world that is filled with all kinds of non-straight lines, wearing somethign like blaze without a pattern to it still stand out like any other solid color will. its lack of definition or more accurately lack of contrast - being one solid color - makes it an attraction point.
out in the real world rarely is there a bloby abscence of some pattern or another, barring a 100% cloud free sunny day where the sky is perfectly blue, or on a snowy field.
which is why blaze with camo, to an animal, is nearly as effective as a natural background color camo pattern. breaking up the shape with the overlay of stick/branch/leaf/rock - terrain in general - images is what makes you blend in and seemingly dissappear when you stop moving.
kinda see what i'm getting at?