A grain of bag!
Something I like to ask actors is if they can change color on command. More accurately, if they could blush if their character was embarrassed, that sort of thing. One actor suggested he could hold his breath and strain himself and whatnot to appear red-in-the-face before the start of a scene, but that's only good for changing colors back to normal. And the last time I remember experiencing that feeling was at least a year ago - I was walking out of the magazine section at borders with a great big stack of things I wanted to read instead of buying, just as one of the clerks I always saw there was heaving an even bigger stack of magazines found around the store back into their proper positions and sighing.
But one thing that is downright admirable about improvisers is the increased chance and indeed, frequent occurance of a performer making an error and publicly shaming themself. And it doesn't matter, not really, and nobody seems to care (I don't mind), but you do see people change color quite frequently onstage. Sometimes you can even see it in their eyes before it happens. They're speaking, they haven't said the thing that they don't want to say yet, but it's coming and it will not be stopped.