The previous post gives you the theory, this website gives you immediate visual. Try moving the mouse over the color wheel and see the hexadecimal representation change. The colors are given web-safe, web-smart, unsafe classification. ANd there are keyboard shortcuts to change the hue (use the j,k,l keys)
The author has kindly allowed the codes to be freely used. I have kept an archive here for future reference.
– a Singaporean teacher's storeroom 🖖