The claim at Quora is close to the mark, although not exactly for the reason claimed. All lenses (including our eyes) suffer from chromatic aberration, a kind of distortion that occurs because different colors have different refractive indexes. In photographs, this distortion results in fringes of color in high-contrast areas. In eyesight, it can increase the difficulty of focusing on certain colors and color combinations.
The textbook Basic Sciences for Opthalmology (Bye, Modi, Stanford, 2013) relates this to the construction and mechanics of the eye:
Chromatic aberration in the eye
In the eye, the dioptric difference between the dispersion of red versus blue light is approximately 2D (Fig. 8.23). Remembering that the human eye's peak spectral sensitivity lies at 550 nm (green), the human retina is deliberately placed such that it is in between the dispersion of white light, i.e., between red and blue. This optimizes the best level of focus specifically for its peak spectral sensitivity. The pupil and the nucleus of the lens also help to minimize chromatic aberration.
In short, the eye is constructed such that it is easiest to focus on green light, which is in the middle of the visible spectrum and has the strongest receptors. Normally, blue light focuses slightly in front of the retina, red light slightly behind. When red and blue patterns are mixed in an image, this chromatic aberration can create an illusion of depth called chromosteropsis (Dictionary of Optometry and Visual Science, Millodot, 2009). In extreme cases, it can cause eyestrain as the eye shifts rapidly in an attempt to focus on the red and blue light at the same time.
There are a couple of other effects that may contribute to the perception that green is a less strenuous color, one physical and one psychological. Blue objects are less visually distinct than red and green, partly because of chromatic aberration, but also because blue cones are located outside the fovea, the best-focused part of the retina with the best resolution (paraphrased from Optics, Hecht, 1987). Meanwhile, the color red signals dominance, aggression, and danger psychologically. While this does make red objects easier to spot, the emotional loading may cause nervous system arousal and stress. (This is a widely-held belief, alluded to in the AnswerBag post, but I should note that it's disputed in a 2004 paper by Robinson, and I don't have the necessary background to evaluate it.)
