
to the Paint Basket family, we are glad you found us.
What You want to do when mixing shadows is first darken the colour as that is often all that is required. If that doesn't get you dark and dull enough, then start adding the opposite colour.
To me it sounds like a classic case of the violet not being dark / strong enough so the yellow instantly becomes the dominant colour in the mix.
Give it a try and let me know how that goes