This is a simple color picker realized in React
The picker roughly looks like this:
You can choose a base color on the layer panel first and then range and/or alpha at bottom.
You can also define your color by typing.
If you're trying to figure out the principle of the web color model, you may refer to:
npm install simple-react-color-picker
Rendering:
import React from 'react'
import ReactDOM from 'react-dom'
import PickerPanel from 'simple-react-color-picker'
...
render(){
return(
<div>
...
<PickerPanel />
</div>
)
}