Dutones
This is a straightforward online tool for applying duotone effects to images. It's useful for quickly converting full-color images into a striking two-color palette.
Colors entries
Duo
Duo is a straightforward, curated collection of color combinations, some of which meet AA accessibility standards. I find it a helpful quick reference for design inspiration, especially when kickstarting a project or looking for specific contrasts.
Coloors
Coolors is a fast color scheme generator, allowing quick palette creation by hitting the spacebar, or deriving colors from images. It's a solid utility for designers needing quick color inspiration or validation.
Happy Hues
Happy Hues offers curated color schemes, presenting them within a live page context. I find this approach useful for quickly visualizing how different palettes perform in a real UI.