That can be cause the colours you're mixing have other colours in them. If you mix a pure cyan with a pure yellow you should get green, but they sometimes put magenta in cyans to make the cyan a prettier colour when it comes out of the tube (cause cyan is a yuck colour to look at). That'd be why. Try to stick with mixing primary colours into other colours. You'll have a better chance of it not spoiling the colour Alternatively, you've also found the dynamic way of making black Pure black is a lifeless colour, so they mix colours together to make black instead cause it's a richer colour. When I took my oil painting course, the teacher wouldn't let us use black.
![[Art] derp](https://storage.googleapis.com/paperdemon-prod-la/submissions/thumbs/art_img_thumb_31409_0cac18522bf72dcb45b624eb1e3239cf5ebd785f64dbc.jpg)
stuff like that happens to me.