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I'd like to have a colour jitter option for custom brushes to create more colour variation especially with the luma stamp options.
Please, pretty please :0)

this one is on my wishlist too.
but...
TVP always has some workarounds
you can get close to this by creating an anim brush of say 255 frames
of which each frame has a different grey value (so going from black to white in 255 steps, to create such a brush you can use the color adjust FX )
now in the brush panel set the second color setting to 'luma Stamp' and set Anim to say 'Random'
now if you draw with this brush color will vary randomly between the current A and B colors!

Thanks Peter, that's not a bad idea.
In this instance I'm already using the brush animation in another manner, but I must admit I hadn't thought about using it for colour variation.