Colorless, uncolored, achromatic mean without color. However, they are not freely interchangeable.
Colorless is applied to something that is transparent or to something that is bleached, blanched, or pallid.
Uncolored is applied to something that is left in its natural state or is not dyed or stained or to objects which have not been touched or touched up with color.
Achromatic is applied to something that is free from any of the hues in the spectrum or from any hues formed by combinations of these or that gives images which are free from extraneous colors produced by refraction.
A color (in its inclusive sense) may be chromatic or achromatic: if the former, it has a hue; if the latter, it has not and is, therefore, white, black, or a pure gray.