The most useful generators are the ones where you upload a photograph (or indicate the URL of a photograph) and the online tool generates a palette from the image. I selected the Color Palette Generator on the CSS Drive website for this article.
The first use of the tool, if you are a painter, is to generate a palette from your reference photograph. This gives you a good indication of the colours and hues you could use for the painting. This is interesting because the palette generated may be different from your usual palette. This way, you can grow your colour vocabulary.
A second use of the online palette generator is to create a palette based on the final painting. If you do that with several of your paintings, it may show you your colour bias.
|Relaxing at Mevagissey - Oil on canvas by Benoit Philippe|
You get even more interesting information when you compare the palette obtained with the final painting with the palette generated by the tool from your reference photograph.
Oil painting Watercolour Painting technique Color Colour Color Palette Generator