Tertiary Colour in Paint

[messiahandrw]

Does anyone know what the tertiary colour in MS Paint is used for? If
you don't know what I mean, try control clicking on a colour in paint.

 

[David Candy]

I'll have a guess. It's to change the background of the colour picker in case you choose the same colour of Windows.

 

[Rishi]

With tertiary colour you can paint with three colours at a time without
changing the colours. For example, if you press down control and draw a line
you can use tertiary colours. If you right click and draw a line you will be
using the background colour. If you left click and draw a line you will be
using the foreground colour.

So basically it gives you the option of using 3 colours simultaneously
without having to keep changing your primary colour.