Because the eye has almost no colour sensitivity at low light levels. The photographs come from sensors integrating for hours; the eye integrates for a fraction of a second and sees in monochrome at that brightness.
This is the most common disappointment in the hobby, and it is physiology rather than equipment.
How the eye works in the dark
Two kinds of receptor. The ones that see colour need considerably more light than a faint nebula provides; the ones that work at low light see no colour at all. Below a threshold, everything is grey.
What that means at the eyepiece
Faint extended objects appear as grey patches with structure. The structure is real and rewarding, and it is what visual observers learn to see — but the colour of the photographs is not available to the eye at that brightness.
Where colour does appear
Planets, the Moon, double stars — all bright enough to engage colour vision. Some observers see a green cast in the brightest nebulae in a large aperture, and a blue-green in certain planetary nebulae.
How to enjoy what is actually there
Averted vision: looking slightly to one side of the object puts its light on the more sensitive part of the retina, and faint structure appears that vanishes when looked at directly. It is a technique rather than a purchase, and it is the single most useful thing a beginner can learn.
The questions that keep arriving
Will a bigger telescope show colour?
A little, on the brightest objects — the green of the Orion nebula becomes perceptible in a large aperture, and some planetary nebulae show a blue-green cast. Most objects stay grey at any size.
So are the photographs false?
They are true records of light the eye cannot register, in the same way an X-ray is. What they are not is a preview of what an eyepiece will show, and listings that use them as one are misleading.
Last reviewed 17 September 2026