Your eye can only resolve points at beyond a certain arc angle, below which two close points of light appear as a single point. It's to do with the spacing between the photoreceptors in your eye (they are individual units that act as a single eye, not a single sensor, i.e. your eye has a resolution of its own), the wavelength of the light coming in, and some neurological stuff. Physics and biology.

Edit: wanted to add that all color TV's are made of a matrix of three color elements, usually with 2x the number of green versus red and blue. If it looks like it's one color, then there's usually a diffuser in the way, or you need to get in closer.