Make checkbox and radio button inner symbol color less stark
We've gotten some initial feedback that the new radio buttons look like creepy eyeballs staring at you. This commit blends the inner dot's color with that of the surrounding color to reduce this effect. Contrast regarding which items are checked should still be there due to the color and lightness difference between checked and unchecked items; however the contrast within the control should be pleasingly reduced.
Checkboxes get the same treatment to avoid them oddly using a different color for their inner symbol.