Will the HTML colour grey (696969)show in all browsers if it used as a font colour as it bis not one of the web's safe colours, and if not will it default to something else?
Yes, there is no reason why the colour #696969 should not show in all monitors. Only if a person had an 8-bit monitor (most have at least 24 now) would the colour dither as the monitor would try to add color from the safe list to adjust it.