Enter how many colours(up to 9) you want and then wait, and then you'll have a palette. You can enter "random" to get 1 to 9 random colours. To use these colours, right click and then click on Save image as... and then use a program with a colour picker to use them.
I created a sprite with 21 costumes, each different saturations, and then did a script where it would make (answer) clones and change the costume, brightness, and colour from -100 to 100. Feel free to use this for whatever you want, credit is not necessary but it is appreciated.