IPA: /ˈkʌlərləsli/
KK: /ˈkʌlərləsli/
In a way that lacks color or vividness; without any color.
The painting was colorlessly done, making it feel dull and lifeless.
Colorlessly → It is formed from "color" (from Latin "color", meaning hue or appearance) and "-less" (meaning without) and "-ly" (meaning in a manner). The word "colorlessly" means in a manner that is without color or hue.
Think of being 'without' ('-less') 'color' — that's why colorlessly means lacking color.