Why are glasses a different colour from overlays?
When you wear glasses everthing you see is coloured, but you are often unaware of the colouration because you adapt to it and make allowances for it (for example, the colour of light from a normal household light bulb is very yellow in comparison to daylight, but you are never aware of this). When you use an overlay only part of what you see is coloured and the eyes are adapted to white light. The way that the brain processes what you see in the two circumstances is very different.
