I think red font on black background will cause the least eyestrain from a quantum physics/chemistry perspective. Red has the least amount of energy and hence it's the least likely to hit electrons and to cause them to move into higher energy levels and to bounce them off which tends to produce ions (and producing ions tends to cause unwanted chemical reactions). Red is basically the least destructive color which is why it doesn't destroy your film during development but other colors will.
Also whenever something emits light it doesn't emit one color, it emits a distribution curve of frequencies. One of the reasons why CRT monitors and televisions were bad for your eyes if you sat close to them is that they emit more X - Rays than LCD monitors do. However, the color you see is determined by which frequency/frequencies are emitted with the highest intensity from the particular light source you are looking at. Light emitted from your LCD monitor (just like any other light source) does emit some UV and it does emit some X - rays, though with LCD monitors its not as intense with CRT monitors. However, red light will tend to emit less ultraviolet and X - rays than white or purple light. And UV and higher energy radiation is more damaging than lower energy radiation.
Most of the light that we naturally see is reflected light, we hardly ever look directly into emitted light. Looking into a light bulb is bad for your eyes partly because you're not looking at reflected light, you're looking directly at emitted light. Likewise, looking into a monitor is bad for your eyes for the same reason. This is why a black background is optimal for causing the least amount of damage, you want to reduce the overall amount of light being directly emitted into your eyes. Also a black background will also reduce the U.V. And X - rays being emitted into your eyes.-reply by corvette