adjective.
Lacking animation, variety, or distinction; dull. synonym: dull.
The Century Dictionary and Cyclopedia
Destitute of color; not distinguished by any hue; transparent, blanched, or entirely white: as, colorless water, glass, or gas; colorless cheeks or hair.
In botany: Having no other color than green.
Pale or hyaline. Jackson, Glossary.
the GNU version of the Collaborative International Dictionary of English
adjective.
Without color; not distinguished by any hue; transparent; ; a colorless gas.
adjective.
Free from any manifestation of partial or peculiar sentiment or feeling; not disclosing likes, dislikes, prejudice, etc..