Simple curiosity here, tinged with some practical concerns because I get caught out by this occasionally.
How come Color.DarkGray is lighter than Color.Gray?
This behaviour is also shown in CSS where the property color: darkgrey renders #A9A9A9 and color: grey renders #808080.
Wikipedia has some information on the subject. It sounds like a lot of the named color definitions come from X Windows System. On X, "Gray" is actually closer to "Silver". However, the W3C defined Gray (more appropriately?) as RGB 50%.
Here's some more Wikipedia on the subject:
Perhaps most unusual of the color clashes between X11 and W3C is the case of "Gray" and its variants. In HTML, "Gray" is specifically reserved for the 128 triplet (50% gray). However, in X11, "gray" was assigned to the 190 triplet (74.5%), which is close to W3C "Silver" at 192 (75.3%), and had "Light Gray" at 211 (83%) and "Dark Gray" at 169 (66%) counterparts. As a result, the combined CSS 3.0 color list that prevails on the web today produces "Dark Gray" as a significantly lighter tone than plain "Gray", because "Dark Gray" was descended from X11 – for it did not exist in HTML nor CSS level 1 – while "Gray" was descended from HTML. Even in the current draft for CSS 4.0, dark gray continues to be a lighter shade than gray.
W3C color keywords:
DimGray '#696969' (105,105,105)
Gray '#808080' (128,128,128)
DarkGray '#A9A9A9' (169,169,169) //equal to X11 DarkGray
Silver '#C0C0C0' (192,192,192) //close to X11 Gray (190,190,190)
LightGray '#D3D3D3' (211,211,211) //equal to X11 LightGray
Gainsboro '#DCDCDC' (220,220,220)