When they say red is the 1st colour to disappear under water, it occurs due to red being the shallowest penetrating light of the colour spectrum. Red light only penetrates below water around 10-15m (dependent on other factors like sun position, water clarity, water calmness). Red is followed by pink/orange and yellow at around 30m with blue penetrating the furthest. Obviously a red coloured lure, looks red to us as it reflects red light. Below 15m there is no red light to reflect so it will basically look black.
Cheers,
Allan