How to find out the derived color relative to the main one in LESS/SASS?

Question

css

The css preprocessors have a lot of possibilities for working with color. You can make it darker, lighter, etc. But how can I get another color #E6575B
having some basic color #ff0000 , from which I will calculate all the rest ? Will it be darken(#ff0000, 10%) or lighten(#ff0000, 50%)? How exactly to get the necessary transformations?

Answer 1

razorjam.github.io/sasscolourfunctioncalculator

Answer 2

source code .
// EDIT
For lazy people who don't like to use search :) .