@drwpow there are some nice ones like #ColourPicker on #Linux, but if you need something beyond "what color is this pixel" and/or "how does #00FF00 & #Ff8000 on #000000 look like?" then https://color.adobe.com is propably the way to go...

Unless you do industrial design for products, then you basically need #RAL and/or #PANTONE reference #colours.

Also @randomColorContrasts is a cool bot sometimes offering good and inspiring colour pairs...

Today I found out about #windows #powertoys and #colourpicker: https://github.com/microsoft/PowerToys/releases/tag/v0.66.0