Fix documentation about colors in formspec

doc/lua_api.txt

@@ -970,7 +970,7 @@ textlist[<X>,<Y>;<W>,<H>;<name>;<listelem 1>,<listelem 2>,...,<listelem n>]
 ^ x and y position the itemlist relative to the top left of the menu
 ^ w and h are the size of the itemlist
 ^ name fieldname sent to server on doubleclick value is current selected element
-^ listelements can be prepended by #colorkey (see colorkeys), 
+^ listelements can be prepended by #color in hexadecimal format RRGGBB,
 ^    if you want a listelement to start with # write ##
 
 textlist[<X>,<Y>;<W>,<H>;<name>;<listelem 1>,<listelem 2>,...,<listelem n>;<selected idx>;<transparent>]
@@ -996,7 +996,7 @@ box[<X>,<Y>;<W>,<H>;<color>]
 ^ simple colored semitransparent box
 ^ x and y position the box relative to the top left of the menu
 ^ w and h are the size of box
-^ colorkey (see colorkeys)
+^ color in hexadecimal format RRGGBB
 
 dropdown[<X>,<Y>;<W>;<name>;<item 1>,<item 2>, ...,<item n>;<selected idx>]
 ^ show a dropdown field