This patch adds new 'blending' functionality to the color picker (both the dedicated tool and the ctrl-activated one) along with the associated "blend" slider to the color picker's tool options GUI.
Inspired by traditional painting, color picker blending changes the way that color pickers have traditionally worked in Krita and other similar digital art programs; instead of completely replacing the user's current brush color with a newly sampled color for a given pixel or radius, color picker blending allows the picker to act more like a physical brush or sponge by "soaking up" some portion of sampled color (based on the "blend" option slider) and mixing it into the user's brush color. In practice, this gives artists another convenient way to mix colors "off canvas", independent of brush shape, opacity, and stroke location. This feature can also be used in combination with other classic digital painting techniques like semi-transparent glossing or smudge mixing for, in my biased opinion, great results and a very paint-like feel.
It's worth noting that, as of now, the color picker seems to "resample" as the user moves their mouse around - this is a mixed blessing. With a relatively low blend value it can feel great to "dip" you color picker into a color and drag it around as it picks up more and more color, but with a higher blend value it can sometimes be easy to sample more color than you intended to, especially when using a drawing tablet as it can be easy to make small movements when you tap your pen against the surface. This is a minor issue and can be mitigated by being careful or using lower blend values when using a tablet, but a future "fix" could involve slowing down the rate at which the color picker "resamples" as you drag it around with some kind of timer or leniency area.
I put together a small and informal demo video: (Sorry for the audio quality issues).
Krita Feature Prototype - Color Picker Blending
Krita Color Picker Blending Prototype Feature - Demo Painting Timelapse (No Audio)
Finally. I'd also like to mention that I created this feature patch together with my brother and friend Eoin, and for both of us this is our first patch submission to an open source project! What better project than Krita?