It's worth noting that since octos see in shades of grey, and don't see red well, that the stick is going to appear "bright" like white or light grey if it's blue or green, and dark or black if it's red... so how visible it is will more depend on how bright or dark the background is... It's rather like if I look at a stick that's painted with infra-red paint: it looks black to me, not invisible, but to an infra-red camera, it looks bright, or infra-red-colored, or whatever.
It's still an interesting question: do octos like sticks they see as "bright" or "dark," but it's only going to have trouble seeing it if it's a dark stick against a dark background. But it might indeed see "dark" as more threatening, since octos turn dark or ink when they're alarmed.
Of course, I do advocate using this when it's useful to appear red to humans and dark to octos: I was hoping the red plastic tubes would look like "this is a nice, dark place to hide" to an octo but let humans see the octo lurking, and using a red flashlight can make a shy nocturnal octo think it's safe and comfortable to come out, but still let its owner have some light to see it by...