You can see color in objects if you have a big enough scope but that's not being practical. In Steve Kennedy's 24" and 28" dobs, numerous planetary nebulas are in color. You just need enough light to stimulate the cones in your eyes. If you read "Seeing In the Dark" by Timothy Ferris, he describes the Tarantula nebula at the eyepiece in a huge observatory scope and said it was brick red. But like I said before, under most viewing you rarely see color, so it just depends.