1 Monitors vary greatly in their color intensity. 2 For emissive rather than reflective displays (that is, monitors rather than paper), increasing ambient light decreases contrast. I've found a huge number of websites are very unreadable not only on mobile devices (which tend to get used out-of-doors) but on desktop and laptop screens if there's a high level of indoor lighting. Worse if there's low-angle early-morning or late-afternoon sun.