First, scanners are not accurate. The colours you get back will not be the same as the colours of the original image.
Second, the LDConfig.ldr colours are not accurate. They are best-approximations to the actual LEGO colours, adjusted to look 'right' on a typical computer monitor. Not that monitors are particularly accurate either... :-)
Third, in this particular case, the sticker is supposed to be the same colour as the part it's being applied to, so it is entirely reasonable to use the LDConfig colours for it.
Second, the LDConfig.ldr colours are not accurate. They are best-approximations to the actual LEGO colours, adjusted to look 'right' on a typical computer monitor. Not that monitors are particularly accurate either... :-)
Third, in this particular case, the sticker is supposed to be the same colour as the part it's being applied to, so it is entirely reasonable to use the LDConfig colours for it.