There are a lot of color pickers/generators out there. Most I list here allow you to enter in your own color like you specified:
- ColorKitty - Palette from image
- Cohesive Colors - New palette formed by old palette + color overlay
- Colour Lovers - Palettes based on color or combination
- Handy Colors - Palettes from named colors (handy for testing) and some pre-made palettes
- Picular - colors from search terms
- ColorBox- Generator by Lyft
- Data Color Picker - Generator ("specifically for data visualization")
- Colormind - Generator that uses UI to show the colors
- Couleur - Generator
- Palx - Generator ("specifically for UI")
- Geenes - Generator
- Color by HailPixel - Generator
- ColourCo.de - Generator
- Adobe Color CC - Generator
- Coolors - Generator
- Palette App - Generator
- Color Supply - Generator of 2-color palettes
- Poolors - Color combos least used by designers.
There are also some sites that give you pre-made palettes, including those of popular brands
- Google's Material palette generator - Generate material color templates according to their design guidelines (well, close)
- Brand Colors - Brand colors
- Happy Hues - Palettes that you can preview applied to a webpage
- Colors.lol - Overly descriptive color palettes.
- Culrs - Picked palettes based on color type
- Poke Palettes - Palettes based on Pokemon
- Color Leap - Palettes based on time periods
- Found Color - Palettes from curated photos
- The Day's Color - New palette daily
- Minimalist Color Palettes - A great selection of hand picked palettes
- Website color schemes - Color schemes with adjective descriptions
- Colors - computer generated palettes
- Color Hunt - Mutliple palettes daily
- Conic.css - Conic gradient pre-made palettes.
There are also some sites that offer gradient combinations which you can get the color codes from:
- CSSGradient - gradient generator
- uiGradients - probably my favorite gradient site
- HD Gradients
- Hypercolor
- Grabient
- Webgradients
- Eggradients
- Color Designer
- Gradient Magic
- Colors - AI palette generator based on text prompts
Or you could let AI choose some colors for you using AI Color Wheel.
I also like to look at the chart below (pulled from here when considering which colors to mix (usually on top of the gradients above) for best contrast:
P.S. Similar but different, some tools to interpolate between two colors: