Back in the days I worked a while as a web designer, spent my days in Photoshop, learned all the shortcuts.

So I was showing the design to this client who always wanted to modify things, and he said he doesn't like the orange a lot and if we can tweak it. I had a red layer, and a yellow layer over it with opacity, so I clicked on the yellow layer, and started pressing random numbers on the numpad (pressing numbers changes the value of the layer's opacity) so the colors were jumping randomly from red to orange to yellow and the hues in between, finally I settled back on the exact value that was before, and that seemed to satisfy the client. The color was now perfect.