1. Hexcolorpedia | https://hexcolorpedia.com/
Hexcolorpedia is a free website that gives you information on any color that you give it. Just input the hex code and it will tell you things such as it's readability, color schemes using the color, blending with other colors, and more.

2. Coolors | https://coolors.co/
Coolors is a website that shows you different color palettes and allows you to save specific colors from each one that it generates to help you create your own unique color palette. They also have a library of pre-made color palettes that you can browse.

3. Dopely | https://colors.dopely.top
Dopely is an incredible multipurpose color website that includes tools such as a Palette Generator, Gradient Generator, Color Wheel, Color Mixer, Color Converter, Color Toner, Contrast Checker, Color Blender, Color Extractor, Image Palette Maker, Color Picker, Color Harmony, Color Name Finder, Color Blind Simulator, and even an Image Hue Changer. These tools are all free to use and don't require a sign-up!

4. LearnUI Contrast Accessibility | https://www.learnui.design/tools/accessible-color-generator.html
This is my pick as far as contrast checkers go, the tool gives you the option to check the contrast of two colors and see if they meet AA or AAA standards for visibility. It also provides alternate colors to what you have that meet the set requirements. Measuring the contrast ratio is key in ensuring that your designs are accessible and legible to all who see them.