Cyan is in the 'blue/green' range... Actually comes from a greek word when translated means; transliterated: kżanos, meaning "dark blue substance".
It's pretty much one of the only two options for 'light' blue in 16 color pallete. True light blue usually gets used for other things onscreen like the sky or water shading.
If you are slightly color blind it might look 'greener' to you, than towards the blue spectrum...
Infact, cyan has been used on Graham's hat since the early games, because light blue was used for water or sky instead.
Also the window border, is not even the same shade used in the 256 color games (or at least the dominate color)! They use a lighter powder blue, along with several other shades lighter and darker (depends on the game)...! Also those two shades of blue in the border are the ones you generally find in the sky or water in the 16-color KQ games!
This is about as early of a Graham you can go for as far as in the Artwork, from the very first release of King's Quest;
Also to say that 'cyan' is 'greenish' could be almost as mistaken as saying that it is true 'bluish' as well! It's certainly lighter than both blue, and lighter than green... But if you are comparing to other standard colors in the 16 color pallete... It certainly looks more like a 'light blue', than it does to a 'light green'... This is probably the reason why it was historically called 'cyan blue', rather than 'cyan green'.
It's also probably why that particular shade of 'cyan' is also in modern usage called 'aqua', which literally means "blue".
The words "aqua" and "cyan" are used interchangeably in computer graphics, and especially web design, to refer to the subtractive primary color "electric cyan". Traditionally that color, defined as #00FFFF in hex, or (0,255,255) in RGB, is called "cyan", but X11 color names introduced the alternative name "aqua". Later, W3C popularized the name by using it in the named color palette of HTML 3.2 specifications.
Funny thing is 'light blue' is up to interpretation! As it comes in different shades, tints, tones and hues!