Sight is an ability present in Spore exclusive to eyes. It is purely aesthetical and only affects the player's creature during the Cell Stage and Creature Stage while the rest of the stages will play unrestricted.
In both the creature and cell stage, if the graphics effects setting is on low quality, blind creatures or cells will still have color vision although the field of vision will remain blurred around the edges.
Originally, the game designers planned to have a varying array of eyes with different capabilities, however this idea was dropped. Now, every eye in the final version of Spore is only different in appearance.
In the cell stage, having eyes enables color vision and allows to see further. Without eyes, parts of the screen edges are black, but the visible area is still large enough for it not to be a major hindrance.
A Maxis-created cell with sight.
A Maxis-created cell (modified by the player) without sight.
In the creature stage, not having eyes greatly restricts the visible area and makes vision much more desaturated.
A Maxis-created creature with sight.
A Maxis-created creature (modified by the player) without sight.